This will sound facetious, but I recommend getting her a cake she likes.
I don't know if is too late to ask questions or do sleuthing, but if there was some kind of cake from her past she really liked that she hasn't had in a long time that might be ideal. Like for my wife that was ice cream cake which isn't as much a thing anymore as it was in our childhood. For me that is certain recipes my mom made in my childhood.