When you're as rich as her you get "the help" to do shit like shopping and stuff, so she most likely never leaves her home unless she's going to some event that has security guarding her.
Find a job opening in her house then kill her, simple as
Variations on that should work on any rich fuck
I've seen ads for like private bodyguard and shit just posted alongside regular jobs, that specifically is even better because they literally give you a gun