Breh...
Dude dropped his wallet. She's basically joking that he's lucky he noticed it because she could've taken it and paid for her nails.
No different than someone unknowingly dropping a $20 and you going, "shyt...you're lucky I'm nice; drinks were about to be on you tonight" before handing it over.
Doesn't mean she wants him to pay for her nails or that you want that person to pay for your drinks. It's just a simple joke for someone that almost lost their money.