Oh, no, I didn't mean it as it's something that has to be done, tho rereading my comment i can see where that's implied, I meant it more as:

Paying for the cab fare does not suddenly make the person you slept with a prostitute (that's what i got from OP's comment. That as soon as money was added into the equation, he's suddenly with an escort), hence "that's another story".

It isn't a must on your part to cough up cash for the other person at all, but I dunno, I feel like the least you can do is offer to pitch in if it's not gonna inconvenience you and she's not being rude about shit (in this case, it's hard to tell for me if she was); but that's a me thing. When you're raised to offer your help when you can and you lived in the not-so-nice parts of town most of your life...yeah, I tend to ask anyone that's with me if they can make it home alright and offer to help somehow if I'm able to. I understand if people can't or don't wanna do the same, tho admittedly, I sometimes forget that it's not like, the standard response, you get me?