She has the right to do as she pleases, based upon her needs and her responsibilities.
On the other hand, so do I.
Personally? I would say,
"No problem. I don't think there is anything wrong with being an escort, nor with paying one. (ie myself). My preference would be not, but baby if it important to you I support your choice."
Then I would ask her to explain to me the reasons why she was considering it and we would discuss it.
Afterwards I would look deep into here eyes and with a playful twinkle in my eyes I would ask her.
"Tell me about your services...?", and
pull her towards me...
...
ahem, fast forward two minutes
But my answer would also depend upon the girl. For some girls, her reason for asking would be as some sort of passive-aggressive test. For others, it could be part of any one out of a large paradigm of relationship dynamics.
But for the most part, I really wouldn't care.
(Actually, it would be a turn on to be stepping one more step further away from society's norm. It's good to be bad!

)
fj