It's just something she's developed ever since puberty. Renee's sixth sense just allows her to just know when her cleavage is filling the eye of a stranger. For her job working at a bar, it's been a great asset. A quick turn and a sultry stare or wink gets the person who's getting the eyeful in a good enough mood to tip more than they possibly intended to her. Even tables she doesn't cater to try and give her a tip. It's to bad Renee can't even tell when she's giving to much of an eyeful. A wide neck & shoulderless sweater in her size sometimes gets itself astray and lets a nip slip out.
Nude renders attached below.

Note: yup, these are the two renders I had issues working on. Learned a thing or two from trying to make a shoulder-less sweater. Even now certain things didn't come out as intended in the final renders. I'd like to two a more detailed post about creating these renders if anyone would be interested.