And things take a turn for the worse...

I'm nervous that when I talk about all this with T tomorrow I won't have time to tell her all of it and I'll have to wait a week to discuss some potential things I can do to make this situation better. Is the situation serious enough to justify me potentially asking her for another session on Wednesday if we don't have time to finish talking about it?

Yes definitely!

just want to send so many hugs your way. that kind of stuff from parents can be so so crazy making and hurtful. I hope you are able to go in to your T and just be able to talk about this . it sounds so painful. do you think you could have the courage to ask for an extra session if you don't have the time . I hope your T has that ability .I know some dont

I didn't see this . it is serious enough. and wow I have so much admiration for you saying the things you did to your parents and sticking to your guns. just remember you are your own person. and individual from your parents .and even if they never ever admit to the hand they have in your pain .you can still move on and grow

She has the ability; it's just that she doesn't want me relying on her. The last time I asked for an extra session (for an "emergency" much less dire than this one), she agreed reluctantly, although she did point out that it might be helpful for me to exercise my "independence" muscle and deal with that alone and wait a week to tell her about it. I disagreed, and the extra session helped a lot. But she did say that if this is going to become a regular occurrence, then perhaps I need more help than she can provide and recommended a DBT skills group ($130 a week, on top of the $110 I already pay her; no thank you). But I feel like this situation is important enough that she would think it was okay.

Should I then preface the whole discussion with, "I don't want to rush this, so if we run out of time to get to the important stuff, can I have an extra session tomorrow?" or should I just ask at the end if I need it?

this sounds like a good way to approach the situation. I don't see you ad depending on her to much or giving up your independence . you did a very brave hard thing .and I have been there and having a response such as you had from your parents can easily rock your world and confuse your reality big time .

I didn't do that brave hard thing on purpose; there was anger there and I just couldn't stop myself from letting it out. It would have been smarter to be not angry about it and sit down and have a calm discussion about it if that's what I wanted to do. It would have been better if it hadn't been in the car. When my mom started crying, all I wanted to do was go wrap my arms around her and hug her and say, "I'm sorry, Mommy. I love you. I'm sorry I hurt you." Because I know I did. But we were in the car. So that wasn't possible. (And yes, I KNOW she's the one who needs to apologize for hurting me, but I do understand why she's in pain too. We all are.)

But yeah, definitely confusing my reality.

So should I ask T at the beginning or after?

And ugh, what if I ask her before and she says no? Then that would derail the whole session. I think maybe asking her at the end only if I need it might be better, yes?

I don't have anything useful to add regarding your confrontation with your folks. I only wanted to send some good vibes your way. I have had similar exchanges with my mother and I hate them. More power to you.
Regarding asking your T for additional time, may I suggest the type of phrasing I was taught to use for recruiting volunteers?
"When will you" instead of "Will you."

Or in this case, if you ask at the beginning, "When would you be available to help me finish processing this if we don't get through it today?"
Or if you wait until the end, "I don't feel like we got through everything I needed to discuss and it feels too urgent to wait until next (insert session time here.) How soon could you meet with me again?"

I'm sure you could phrase it better with your own personal style. Of course, you can't help it if she doesn't have time available, but asking reinforces how important it is to you and gives her a chance to offer alternatives to help you in the meantime.

I think that even though it's an important thing to process, given what your therapist said about extra sessions last time, there is a possibility that she has pretty strict boundaries about extra sessions, so it doesn't hurt to be prepared for that response from her. If you need more than she can give you and the DBT group is too expensive, I think it would be reasonable for her to help you figure out other solutions. I do kinda like L4p's assertive wording suggestions. Just because your t might not be willing to do as much as you need doesn't mean your needs aren't legitimate.