According to the transcript, she states,
Among the scrolls that were found in the caves at Qumran near the Dead Sea, we have a very large and very famous Isaiah scroll, which is now in a museum in Jerusalem. On the scroll there is a gap after Isaiah 39, and a new column starts with Isaiah 40. So it seems to signal some sort of implicit recognition that there's a difference between these two sections. They are not the same unit, not the same author perhaps.
I was surprised by this because my impression (from where?) was that there was no evidence from antiquity of a Jewish tradition separating these books.
I was attempting to to figure out what this looks like and to what extent it is distinguished from section markings within the portion consistently attributed to the 8th C. prophet. This amazing website has beautiful pictures of 1QIsaa. The division between Chapters 39 and 40 is, in 1QIsaa numbering, between 32:27 and 32:28. It appears to me that 32:28 (= 40:1) is actually on the final line of a column:
נחמו נחמו עמי יואמר אלוהיכמה
Comfort comfort my people says your God (40:1)
דברו על לב ירושלים וקראו אליהא
Speak tenderly to Jerusalem and cry to her (40:2ab)
Then a new column (33, after what appears to be a normal break necessitated by space):
כיא מלא צבאה
That (?) her warfare is ended... (40:2c...)
Am I looking at the wrong document, or reading it wrong, or what is she talking about? Is there indeed an indication that the scribe recognized Isaiah 40 and following as somehow separate from the preceding chapters?