I'm still new to this whole poly thing, but a couple of things sent up HUGE red flags:
She's only 21 and got kicked out of her parents house - Most parents don't just kick out their 21yr old daughter, especially when she is going thru something major like a divorce.
She is getting a divorce, and her baby is with the husband - again, not typical.
Combined the above two and red warning lights are added to the red flags. This is just a strange situation in itself.