She was sad after she accepted £120 in exchange for sex. But did you make her sad? I bet she would have been even more sad NOT to make the deal. So if you had not booked her, her life is a bit worse. So it is reasonable to book her often. It is her tough life that is making her sad, your £120 made it a tiny bit better. (Unless she was truly forced, which is not what you think and you are the one who met her).
I remember bargaining for carved items in a poor country. $10 he said. $1 I said. We agreed on $1.50. You're killing me he said. But he wouldn't let me leave. He wanted my $1.50 more than he wanted his carved animal. I wanted his carved animal more than my $1.50. Deal.
This girl wants your £120 more than she wants 'not' to have sex with you. Deal.
There are struggling people in this world. It is good to help them. I don't know her. But I bet she is in the top half of those on the earth. If you want to help those in deep shit, send money to Nepal. And as long as they are not underage, forced and so on, pay prossie's to fuck you if you like. Make them a bit happier.