hi! you're so right about the overly nice ones you have to watch out for. Too often, people are very easily gullible and dont have a clue when they're dealing with snake-like behavior.
The best bet I still feel is to go on with your life- as you seem to have grown from this nonsense, while your hypocrite mother still has deep-seated emotional issues she needs to deal with yet.
When there is any opportunity to show compassion or love to anyone in your extended family-- prove your mother wrong and do it. Like if someone has a baby, send a card and a little gift, if a funeral, then go to it and show your respects-- dont say a word, but just give a warm hug and show you care. People can tell when you have true compassion versus "compassion just for show"
If someone in your extended family has a graduation or wedding, be quick to send a card and acknowledgement. and when any opportunity, show them what 'ya got inside--that you are actually not a monster like your mother said.
You have to be patient-but the opportunities to prove your mom wrong to your family will be coming one by one- and eventually they will see that your mother-- nice as they think she still is, allowed herself to get carried away.
If they can't see through her after all that- then they all have the same type of personality gene your mom has and arnt worth your time anyway.
It sounds like your a cool person to me- and I think you should hold your head up high and go about your life living it as you are destined to-- to learn that the meaning of life is all about loving others, and not about making people THINK you love others - but then backstab them later. If there is such a thing as reincarnation, then your mom may be stuck coming back several more lifetimes--lol!