Great work, Minney! As MKAC said, this is articulate, and shows a lot of thought and consideration. It's pretty clear you know what you're angry about and why, and I don't see you misplacing your feelings here. You're mad at the way your mom was when you were a child -- and you did NOT have a part in that the way you would as an adult.
It's odd to me that your T would be taking a "see it from her point of view" stance considering that's what you used to do up until now, so I wonder if there were crossed signals somehow... as you say, confusing things between you and your mom now versus when you were a kid, and that maybe your T feels as if the anger already came up for you, because it already came up for her. Don't know, but I think you're approaching this the right way.
You do need to process this anger before you can move forward. It would be one thing if you were just angry or were just refusing outright to see it from the other point of view. But I don't see that at all. Sure, you need to see it from both sides eventually -- but that means seeing it from YOUR side too, and that means standing up for the little kid that didn't get what she deserved.
Keep up the good work!