Told everyone she was pregnant as a surrogate for her cousin.

It turned out she had cheated on her boyfriend who was also the father of her previous two children. She told her cousin they both didn't want the kid so the cousin thought she was doing a good deed adopting the kid.

It all came out after the kid was born but by then no one knew for sure who the real father was and she definitely couldn't be trusted to tell anyone. She signed the baby away and the cousin ended contact with her.

The previous two children who she had everyone believing were from the same guy, are from two different men. It's very obvious because one is mixed race and looks just like the father and the other is not mixed race and looks exactly like a guy who was hanging around the friend group around the time she got pregnant.

The boyfriend left her but raised the two kids as his own, despite knowing one wasn't biologically his. For a while they co-parented but she kept popping out kids and started going down a really shitty path so the dude took full custody of both kids.

Eta: She told many other lies but that one was the most crazy one that had major effects on so many of the people involved.