[Double-bitted battle axe to apply forty whacks to my long-winded post]
Certainly fear is at the root of pretty much all insecurities, but don't forget that the topic of this is the poll... and the poll is only about Dora's first day of therapy. I'm just more of the belief that it'll take more than a day to crack through her walls of denial and get to those fears... which would make the summation of her first day denial.
But hasn't Dora got a history of being thin-skinned to the point of a single cell layer when the right buttons are pushed (Web page, Underpants, Hitting on Marten, etc.)? I guess what it really boils down to is how much self-control she has. Lately, it's seemed to me that's been on a definite ebb. 'Twill be interesting to see.
It's also going to be interesting to see how long before she actually shows up at a therapist's office, since I'll agree Dora's numero-uno, A-#1 at that sort of denial. And, of course, even if she does, there's every chance Jeph won't let us see it, because of any or all of the following:
A) it's not really vital to the plot
B) there're no laughs to be had, and he feels we've had enough of that sort of thing for a while
C) we really want to, and he's decided to apply Brockian Ultra-Cricket audience theory in order to intensify our experience.
I think a lot of that depends on the source. In the few examples you cited, the... trigger, so to speak, came from people that Dora might consider social inferiors or outright rivals (Marigold apparently being, or at least acting younger, Cossette being both a rival and younger, and Faye, well, this whole thing kind of comes back to her in the first place). In speaking with someone who would be presumably older and thus with more presence (although that would be an interesting switch, if Jeph gave us some young wunderkind as a therapist), she might not have as easy a focus for her anger. I see her trying to explain things to her therapist the same way Penelope was trying to explain things to Dora
about her parents. She'll relate the incidents, but to her, she's not (entirely) wrong, so she doesn't really entirely see the need to change.
I don't know. Looking back at what I just typed, it hangs together but... it doesn't seem quite right. I think I'm missing something.
As for how long before her first visit, well, depending on how that number she called works, there's every chance she already has an (initial) appointment time already. Now as to whether she might call them back and ask to postpone or reschedule, well...
I disagree with A) in that I feel that if Jeph would like to keep Dora in the major circle of characters, we'll need to at least see some definite results from the therapy, if only to "rehabiitate" her in our eyes. After all, she's largely come out as the villain of the piece, bar the "spineless Marten" bashing that we won't go into again. So, in that sense, her therapy is vital to the plot, at least in terms of keeping her as a fairly major character within it. If she's just going to fade away, well, then no, it becomes less important.
B) is certainly a possibility, but given how well he handled Doctor Corinne, I have high hopes that he could manage something good with a new therapist as well.
C), well... not much we can say or do about that!