Should I ask this girl out?

I met her at a friends birthday celebration, we had gone up to a club in London. Drink was flowing and I danced with her quite a bit. The day after I asked the friend who's birthday it was if she was single, the response I got was yes but she's not looking. I've kind of taken that as gospel but she keeps popping up in my brain and I can't get her out of my mind. While waiting for a train with another mate, we saw her and briefly chatted while waiting for the train. Later on I told my mate what had happened (regarding talking to the other girl who's birthday it was) and he said that this had happened before with a girl that he had eventually gone on to date (.i.e. she had warned him off). He described the birthday girl as manipulative and suggested that I asked her out directly. I don't know what to do? Do I trust the birthday girl at her word and stay away or do I go for it?