I don't think you should feed her, if you think she is owned.

If you knew she was a stray or she started to get thinner (Like Mr Stray / RB Caramel), then fair enough feed her.

But what if she is on a diet at home, maybe she has to avoid certain food for medical reasons.....

I wouldn't be happy if someone else fed my cats would you. What if someone fed our cats, so they didn't eat the food we provide, we wouldn't be happy !!!

By all means give her a cuddle but I would think carefully before feeding a strange cat.