[[WMG: Just when Riley and Ben are finally about to get together, Emma's mom will show up.]]
Because it's bound to happen at some point, right?

Alternatively...

[[WMG: Emma's mom shows up at some point and reveals that the baby actually isn't Ben's, and that she's here to take Emma away.]]
And after a heart-wrenching episode, Ben finally grows up and realizes that it doesn't matter if Emma isn't his biological daughter--he loves her anyway and won't give her up. The mom is touched, and decides to stick around and get to know this "new" Ben. Hijinks ensue.
* [[spoiler: Partly Jossed, partly confirmed. She does show up but the really is Ben and hers. And after seeing Emma, she wants at least partial custody of her.]]