You can get - not food - but a topical flea treatment like Advantix or something. We always took our dogs to the vet once a year for a check-up, just in case, even when they were older. If the spot doesn't seem to bother her, isn't warm or red, I'd not stress about it, but maybe make a vet appointment just to get her a check-up and make sure everything is okay. She's getting to be older, so it's a good idea to have a vet give her a good going over, and check for issues, etc. You can add garlic powder to her food that will help deter fleas, some folks find that works great.

Does she lick at the spot?