A few things to keep in mind:
Liza is already nearly 12 years older than Judy ever was. That is saying SOMETHING. She was what, 23, when Judy died.
Liza did have a father, a predominatly gay, but thrice married father who had a large influence on his daughter.
Liza in her prime and even slightly past it, could give the best show you've ever seen and like Judy, make it look spontaneous and effortless.
Judy was heard to say when all the kids were young, that she thought Lorna would be the star. Maybe Lorna didn't "need" stardom the way others did.
Vito Russo on Judy - "When she was good, no one could touch her, and when she was bad--and there were times when she WAS bad--she was still better than 75% of the trash that's up there."
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher