I say it has to do with a couple things - and please don't take personal offence at these

1) Do you trust her to be a stripper and not a hooker??

If the answer to Q1 is YES, the move to Q2.
If the answer to Q1 is NO then you have a fundamental problem with your relationship

2) Do you have a problem with her choosing to expose her body to people she is not in an intimate relationship with?

If the answer to Q2 is NO, then there is no problem - be thankful of the extra cash!
If the answer to Q2 is YES - why? It's her body, not yours? Or does the problem with strangers seeing her half naked body stem from an insecurity in yourself or your relationship?

As said, I'm not trying to cause offence or personally attack you - you just have to look at it logically.....