whytry -
You gotta give it a try!
The longer you wait the farther you go into the LJBF zone. If she has a boyfriend and she's telling you about him, then she's probably just looking for a hook-up.
What I don't understand is why did you bring your guy friend with you when she called you to meet up with her at her place? It seems that showing up to her place alone would be a natural way to sleep with her.
Keep in mind, she probably wants to get laid just as much as you do and was probably disappointed to find out her night went up in smoke (so to speak) instead of getting steamy with you in the sack. You should have ditched your friend.
Still, it sounds like her buying temperature is relatively high so you should make your move now.