So was she Shimon Peres's first cousin or not?

She claims she was. Shimon Peres says no.

Who's lying?

Peres also said recently:
"She told me a bit about acting, about love, but she was not an easy woman. She had very strong opinions, was protective of her dignity, and was not easy to converse with. We had a very pleasant talk, but not much more than that. I don’t know much about the world of cinema; we were from different worlds. She was interested in what I was doing, but didn’t speak about it much. I think there was tension between her and her father, though I didn’t want to ask her about it. I didn’t want to go into her business.”

http://www.timesofisrael.com/peres-lauren-bacall-was-not-an-easy-woman/#ixzz3AQfowZLn