She can be safely fixed if she is at least 3 lbs and over 8 weeks old.

Its important for kittens to eat several times a day. I usually free fed my foster kittens who are eating on their own. If they're bottle babies, then I feed them every 2 hours. I'm assuming this one is older though. I would say to just leave food out all the time but make sure there's not an overeating problem .. most cats won't do that though!