It was so easy to lose herself in the haze of blood when offered. Where Drifter led, she followed. And so when he told her he wanted to come, she obeyed and waited for him to offer himself to her to pleasure.
There should be a warning sign at the blood covered cock, but all she could do was quickly gobble him and suck the blood off of him and then move in earnest in hopes of making him come just as the poor boy had.