I want to ask my coworker why she pretends she has two parents
Why do you want to ask her about her parents?
Because she is lying to everyone here
It's bad to be prying into the personal life of your co-worker. Even if one of her parents is no longer still around, she might have a step-parent or another parental figure in her life. You shouldn't assume that she is being dishonest with everyone when you don't know the truth yourself.
I think she is trying to make herself good at her job and I don't give a shit about her personal life. Fuck all of them.
If she is lying, the truth will come out eventually. You shouldn't insert yourself into the personal affairs of other people, especially at work.