Some special needs are harder to deal with than others, OP, and it appears that your daughter has the emotionally challenging sort.
My son has severe ADHD, ASD, OCD and learning disorders, but despite being supremely irritating... he has a sweet, uncomplaining nature and gives off vibes that he doesn't do these things on purpose to irritate us. So even when we get exasperated, and start yelling at him, we feel guilty that he can't help doing what he does. He's never the one attacking us verbally. He's supremely quiet and passive. And IRRITATING. But we love him to bits.
If you're faced with a teen that can't help being cruel because they tend to get punitive and accusatory when upset, and they're always upset... then I can see why you'd grow to intensely dislike them. It's very hard!
I'm sorry. Please try to never give up on her. Maybe she needs a med tweak? A different therapist? You're doing the right thing by distancing yourself at times when you know you two are going to fight.