Ok so I guess we can't hope anymore that Sloane isn't Mark's daughter because they have positive DNA results.
But, I think her randomly coming into Mark's life because she needs a home (and money) for her pregnancy is a little off.
Let's recap- Sloane's mother Samantha got pregnant by Mark (around, what, 18?) and kept her and raised her.
Now Sloane is pregnant at what appears to be the same age that her mom got pregnant at, and her mom has kicked her out. Why? Why would her mom punish her for repeating her, the mom's, history? It makes no sense. Surely a single mother would have sympathy, no EMPATHY, for her daughter ending up in the same situation.
So, either the mother is heartless or the daughter is lying and just wants Mark's money because she knows he's a world-reknowned plastic surgeon who makes a lot of money.