Killer bunnies, gloom, fluxx are fun, but may be complicated for grandma.
Loonacy is fun and fast-paced ( so maybe not for grandma). (Kind of like spot it)
Munchkin loot letter is a great, short game. (Think five minute rounds). It is a love letter derivative, if that's more your style.
Don't go boom is one that I've played with 90 year Olds. They liked it.