I just read this (for the third time) and was struck by how awkward the Flenser / Tyrathect resolution seemed to be. I think it's partly just a slight weak spot in the writing and editing. I looked into the annotated edition for some clues and came away a little unsatisfied.
In Chapter 30 Tyrathect is firmly in control using the radios. But just after Tyrathect reflects on her experience with the cliffs, the very last paragraph starts "He turned". The masculine pronoun there is a sign that it's Flenser again. I missed it on first read.
Just after that last paragraph author Note 921 reads
QU Is this transition to Flenser too abrupt? NO 21Jan91
This note and answer are both from Vinge. It tells us that this was intended as a transition from Tyrathect to Flenser, that Vinge was concerned it was abrupt, and that on reconsideration he decided it was not. Respectfully, I disagree with the author; I find the transition both abrupt and easy to miss.
Things with Flenser get much more complex in Chapter 34 but none of the editing notes really shed much light on the writing of the transition struggle. There's a lot of notes, including from draft readers, but nothing addresses it head-on. Note 1114 is relevant
[vsv] June 4, 1991 Okay now make a big deal of the housecleaning once and for all that Flenser is doing (but why didn’t he do it before — maybe because Tyrathect was not so exposed as she is now in the wake of this final maximum dffort)
"housecleaning" here refers to Flenser cementing control over Tyrathect.
Note 1116 also seems relevant
[vsv] April 13, 1991 IMP Lots more should be made of this scene and managing the conflict before and after. Suggest that Tyra appear consistently subdued after this point, till climax.
My conclusion is that the book could be improved by a couple of sentences showing Flenser wresting control back from Tyrathect back in chapter 30. It's awkward that we go from a deeply poetic vignette about growing up near reflecting cliffs to a transition signaled by a single pronoun.
I love this book and don't mean to be negative; but this little part is a rough edge.