I think Ruby may have eased up on the Sam/Dean relationship a bit since now Sam actually, you know, listens to her and isn't all, "OMG YOU ARE AN EVIL DEMON GO AWAY". Last season, Dean was the only thing she could use to get Sam to pay attention, but now he actually wants to learn about his mind powers of Awesome, so, er, maybe that explains her change in outlook?

because making him look like an insensitive git in front of the others amused her

And whenever they go out to bars or diners to discuss, uh, stuff, and Sam looks like he's going to Get Some later on, she immediately pounces on him and pretends to be his long suffering girlfriend. Sam is not amused.