If you live near where she is buried, then a trip to her gravesite might be nice. I usually try to have a Mass said at our church, too, for any deceased relatives. I like the idea of a PP to eat some of her favorite foods. Other thoughts, do something that she liked to do or play music that she liked to listen to. If you have a clothing item of hers or a piece of her jewelry, maybe wear that.
Hugs, OP.