Maybe do it in a flirty way. I might say, "I don't usually give feedback but a few nice words either way are nice, what do you think?"
If she doesn't have much feedback she might be grateful of it. She's more likely to remember to give you some if she has to keep checking to see if you've left any yet. If she has loads, why the fuck should she bother with you may be her attitude. She's in business: giving you feedback isn't included in the deal, only if she 'feels' like it.
Of course, if you're an obnoxious cheesy bastard that left mud on her floor, wiped your dick on her curtains after spunking in her eye, and filled her face with beer breath before whining for a compliment, you're maybe better off without feedback.