Sounds like the first signs. My vet says they can come into heat as early as 5 months and at 18 months I started noticing changes in my female cat's behavior. She was spayed the next week!
You'll want to have her spayed ASAP if you want to avoid those terrible in-heat yowls, trying to get outside, and possible spraying!

I'd be getting her spayed ASAP also, you'll need to watch her like a hawk now to make sure she doesnt slip out like annz said.

So far this morning no signs of weird behavior from anyone. We are getting ready to travel to my parents for Christmas where she will be kept 2 sets of doors away from any exterior doors, so I think we will be good for the next few days. By the time I get back, she should be out of her first heat if that is indeed what this is, and I can talk to my vet about a time. This is the 4th female cat I've had, and never had one go into heat so soon! I've had her three months and it just doesn't seem possible that it's time already.

Oops......quite a typo I made! Should have been 18 weeks, not months!