I have a friend like this too. She bad mouths my husband all the time to others as a deflection of her newly ex-husband. But in the same token, I really care about her for many reasons, so I won't bad mouth her period.
I just stay polite and kind to all even when I know she's tainted people against me. Whatever. There are also common friends that moved away from her because they recognize she is toxic, and tell me without me bringing it up, because she gossiped to them about my hubs.
OP, it doesn't matter if you get married and have kids; having a toxic mentality doesn't resolve itself like magic.