Well, I hate to be the prude here, but there's no way the sex could be any good for me if I thought my partner was just thinking of someone else. Yeah, "she told her", but someone can only fake it so convincingly; she's abusing the poor girl's heart by play-acting like she's into her. I would've been pretty damn hurt at the "I told you ..." scene and walked out and never spoken to her again. But then again, I have self respect and wouldn't have subjected myself to this in the first place.
Oh well. To each their own. If this is your thing, more power to you.