Ever hear the phrase, "Misery love company" ?
From everything you said, I'm 99% certain that your grandma has a controversial personality. People like that are pessimistic & confrontational by nature spending much of their time focusing on the negatives about everything. This is because she is not happy being happy, so she talks about controversial issues & looks for flaws in others. If there is no current drama in your family life, she will bring up past issues or start on topics just as or more upsetting & the reason she focuses on your mom & not you... is, because you are stronger willed. Your grandma does not know how to break your spirit.
The fact that you said your grandma enjoys going to funerals & seeing people crying, shows that she is pathological.
I don't think your mom needs therapy. She NEEDS to separate herself from her mother & let her rot in her misery alone. It sounds cruel, but what your grandmother is doing is far worse. Your grandmothers mentality of breaking down a person's self esteem & making them feel worthless, is exactly what pedophiles do to children & abusive men do to women. It's not for the same motives, but it's the exact same mind set. To break a person's spirit so you can have control over them & relish in their suffering for your own personal gain.
It sounds like your grandmother's motive is simply to just create drama. We call people like that on the internet Trolls & you know what they say about trolls.
Don't feed the troll.
The only way your grandma will change is if she is punished by separation. Maybe then she will change her ways. The only way your mom will get stronger, is if she continues to stand up to grandma & make her leave when she acts like that.