Dinah is the only daughter of Jacob who is named. She is important, of course, because she is a main character of Genesis 34, which is in turn a pivotal chapter in the narrative of redemption of Jacob's family. Some older commentators, such as John Gill in the 18th century, as well as more recent ones, such as Allen Ross, have assumed that Jacob had only one daughter. Is that the case?
Probably not. But it isn't as simple as it looks. Whether Dinah had any sisters, full or half, we are told, as we will see, but only briefly and vaguely. But we should not expect clarity on the point. It is an easily-confirmable fact that most genealogies in the Bible omit most or all daughters, as I will discuss further down. As I will argue, Dinah was mentioned probably only because of this incident. As we will see, there are two later references to the "daughters," plural, of Jacob (37:35 and 46:7), suggesting that Dinah had some sisters.
The notion that Dinah was the only daughter is never stated; commentators like Gill and Ross infer it. It is supported by the common-sensical reasoning that, surely, Jacob's children were so profoundly important to the Bible narrative that it is hard to imagine that other daughters would not be mentioned, if there were any.
This argument is weaker than it looks, because, as it turns out, very few sisters indeed of some of the most important characters in the Bible are ever mentioned. We are not given the names of any sisters of Abram (other than Sarai); Isaac; Jacob; the twelve sons of Jacob (other than Dinah); the vast number leading Israelites found listed in Gen 46, Num 26, and 1 Chron 4-8, any priests or prophets (that I can recall, though there were a few women who were prophetesses in their own right); and few sisters indeed are listed of the Judahite and Israelite kings (only Tamar, sister of Solomon, springs to mind). Should we assume that among the dozens of brothers that these men had, collectively, they had only four sisters? We are not even given the name of Jesus' sisters; you would think they would be important enough to mention. The point is that we should not expect any other sisters to be mentioned, if they do not specifically figure in any story—and they do not. Dinah is the only one.
Now let's have a closer look at "all his sons and all his daughters" in Gen 37:35. The word for "daughters" here, בְּנֹתָ֜יו or benothaw, is certainly plural. Thus either Jacob had daughters other than Dinah, whose mention was necessary due to her importance to Gen 34, or this refers to the wives of his sons; but "son's wives" are usually so-called in the Bible (see Gen 11:31, 24:51, and Lev 18:15 for just a few examples). I think the most straightforward and probably correct reading of this text is that the plural "daughters" does entail that Jacob had at least one daughter of his own in addition to Dinah.
A similar and more telling text can be found in Gen 46, and it turns out to be very relevant to look at how the womenfolk are treated in Gen 46's genealogy. The genealogy begins by saying that it would be a list of "His sons, and his sons' sons with him, his daughters, and his sons' daughters" (46:7). The list concludes with this: "All the souls that came with Jacob into Egypt, which came out of his loins, besides Jacob's sons' wives, all the souls were threescore and six" (46:26). If you count carefully, you will discover that no women are listed in the tally of 66. Is that really true? Indeed it is: after all, we are explicitly told that "Jacob's son's wives" are not listed. As we will see, Dinah is not included in the count of 33 descendants of Leah.
Again, women are rarely listed in genealogies, and it beggars belief that, generation after generation, there should be nothing but sons, with occasionally one or two daughters mentioned. After all, the lists in Gen 46 are quite explicitly "of sons," not "of children." Women, particularly those who are not wives of important figures or who play no direct role in the narrative, are usually not mentioned in genealogies; any daughters, even of important figures like Abraham, Isaac, Jacob, Moses, David (except for Tamar), and Solomon are not mentioned. When they are mentioned collectively, as in 46:7, they are rarely given individual names.
So the mere fact that only two female descendants (Dinah and a granddaughter, Serah) are mentioned in Gen 46, neither of which is counted in the tally of 66, hardly means there were no others. Indeed, on that specific question, we have most strikingly a clear reference to Jacob's "daughters, and his sons' daughters"—note well, they are listed separately—which are among those he brought "with him into Egypt." (46:7) This is very similar to 37:35's reference to "And all his sons and all his daughters rose up to comfort him". In both cases, the word “daughters” בְּנֹתָ֛יו (benothaw) is indeed a plural form of בַּת (bath)—suggesting on the most straightforward reading that Jacob had at least one daughter in addition to Dinah, and in addition to his granddaughters and daughters-in-law. But only Dinah was ever listed in any of the genealogy lists of Jacob’s offspring, and only a Serah, daughter of Asher, is mentioned in Gen 46 as a granddaughter.
Looking at one last question will help cement this interpretation. Why are Jacob's "sons and his daughters" through Leah (Gen 46:15) numbered at 33, when 33 is the number of males, only, that are listed? If you do not believe me, have a close look. If you will bother to tally up the names listed from Gen 46:9-14 very carefully, including the names Er and Onan (because they are Jacob’s sons, though indeed not his sons which went down to Egypt), you will find that there are precisely 33 names given: four sons, 27 grandsons, and two great-grandsons. If Dinah is included, the number rises to 34; if Er and Onan are excluded because they did not go down to Egypt, the number declines to 31, or counting Dinah, 32.
So we are forced to conclude either that the author of Genesis made a tallying error or that he meant to count sons only, and to exclude not just the unnamed daughters, granddaughters and great-granddaughters, but even Dinah. The text says, "all the souls of his sons and his daughters were thirty and three." (46:15) It is almost as if to suggest that women were not souls (or lacked them). But of course that is not the point. The situation is very similar to the censuses of Num 1 and 26, 2 Sam 24, and 1 Chron 21: women are simply excluded, because the numbering was of fighting men, i.e., of army size. Interpreters do not assume that there were no sisters alongside the brothers who were counted in the big censuses. They assume, naturally, that it's usually close to a 50-50 split, after all. If, therefore, 66 souls went down to Egypt, then it is natural to assume that there was a female contingent of similar size. And if 11 of the males were Jacob's sons, it is reasonable to assume that they had more than one sister. A count of 12-to-1 is possible, but unlikely.
Still, why does the text say specifically that 33 was the number of "all the souls of his sons and his daughters"? We must conclude that tallies of this sort were a thing regularly performed in the ancient near east, and that it was so obvious to the readers of the Pentateuch that such lists included men only and excluded women, that it was not regarded as any sort of contradiction to say that the tally of Jacob's sons and daughters with Leah was 33. The provable fact that Dinah is excluded from the number 33, when that number is supposed to represent "all the souls of his sons and his daughters," suggests that the number of sons alone suffices, as it were, to represent or go proxy for the daughters as well. There is no good reason not to suppose that Jacob, his sons, and his grandsons together had a similar number of daughters by this time. The Hebrews and doubtless other near eastern cultures would not have bothered counting them. We might find this to be annoying, but if so, I hate to break it to you—no ancient culture was politically correct by modern standards.
So we must not apply ordinary modern expectations about how daughters might be described in the text. The mere fact that only one daughter is listed does not mean there were not any other daughters. The reasonable conclusion is that Jacob probably did, in fact, have the plural "daughters" of his own which Gen 37:35 and 46:7 both appear to claim he had.