Still praying for you here. Try if you can to stop searching for the “perfect comeback” or the best way to not let this bother you because I do not beleive that it exists.
Try and remember that the person in your family who’s situation is the most dire is not you…it is your mother. Even though you are sad and depressed and have had lots of therapy…remember what is the most important in the universe is your eternal soul! If you embrace your faith and honor God and attend Mass then your soul is right with God. Your mother is in spiritual danger and this is important to remember when dealing with her.
You will not help this situation by focusing your energy on how much she is hurting you, you need to try your best to focus your attention on praying for her. Try as best as you can to stop searching for ways to cope with your own pain, instead look to prayer to heal your mother’s pain in her soul. I would not seek out her company regularly but when you have no choice but to be in her presence then remember Jesus.
Remember Christ in these moments of your life. Remember people lied about him and hurt him and spit on him and humiliated him. What did he do? He actually prayed for his tormentors because he understood that their eternal souls were in danger. This does not mean we as people need to invite abuse, but we need to pray for our abusers when the situation arises.
I understand that behaving like Christ is not an easy task!!! Far from it! But I think that is where the true key to solving your problem is. Changing my way of looking at people in my life has helped me beyond measure. Try your best to see your mother in a different light, she needs pity. I will pray for all of you. Hope this helps.