We don't know who initiated the encounter. It is entirely possible that this is a case where the woman pursued the man. We also do not know that she was on the verge of passing out at the time agreement to sex was reached (if it was reached).  Remember "It would appear that prior to that she had been able to communicate with others. Although she appeared drunk to the staff at (the bar) ... she had appeared to make decisions for herself". It is reasonable to think that she may have also appeared to the taxi driver as able to make decisions for herself.