Re relationships: I think a close relationship is a close relationship. She has different types of memories of their time together, but he was/is her heart and soul. And a parent loves a child like no one else. I've often said - you don't even know love till you stare into the eyes of your newborn. In a more general view - people get divorced all the time and are fine, but when someone loses a child, typically the parents are devastated forever. It's just different.
Re Nastiness - nope, nothing gives her that right. And maybe she feels safe enough with you to just be raw emotion. It's not kind, or right. But usually these things stem from her own pain. Your story about being yelled back at - she clearly doesn't expect these things. Perhaps she feels omitted? Maybe she believes things should be done "a certain way" and it didn't happen and she's bitter? Maybe she is very hurt that her son eloped? Who knows. The point is that it's coming from somewhere. If she really cared about your weight or race, she probably wouldn't say anything. They're easy things for her to jab you with that can't be changed.
There comes a time in every contentious relationship where you either have to sit down and decide to work through it, or give up and decide that that person is not worth having a relationship with. And again - you can vision it as times you've probably done the same in a romantic relationship. It takes a lot of work, but if two people want to work on it, it CAN be done. It sounds like she feels very lonely, and that may give you an easier "in" to healing.
Also you wrote something that sent up a flag "Thank you for raising this man FOR ME" TRUST ME, her first response to that will be "I didn"t raise him FOR YOU!" No matter how innocently you meant it, it READS like you feel she's handed him over TO YOU. And it will invoke the "Mama Bear" inside all of us moms. Because (God forbid) anything ever happened between you and him, she will still be in his life helping pick up the mess.
So - should she act that way? NOPE. Does she feel justified in it? Most likely. Do you want to move beyond it and try to have a strong relationship with her? Up to you, but I would recommend it. This could be your chance to be the next-in-line matriach of her family. One day she'll be gone and she needs to know that there will be SOME woman who will keep her dear family together. Holidays, birthdays, keeping kids in line, making sure people are respectful of the family name and all that that entails. Moms are proud, defensive and (Deep down) deeply loving. A lot can be learned - about her, her son, her other sons and family members. And maybe she can learn it's okay to let her guard down and be a little kinder.
She dealt with you eloping without a big fuss. I dare say she really loves you both! Same as getting married doesn't come with a manual, being a MIL doesn't either. Everyone is learning and IMO everyone should try to foster the relationship and try to wince off the wounds in hope of a better tomorrow. "Wow! You know when you say that, that really hurts!" Can go a long way to improving the future.
Most people aren't evil inside - they're crying inside. Sometimes that comes out as evil. Sometimes as depression. Sometimes in addictions. Etc etc. If you can find a way to get through her walls of self defense everyone wins.
Patty