Unfortunately, there's almost nothing you can do to help her right now.
Every tom cat within a square mile will be looking for her. (literally) And she'll be very interested in getting out. I've even heard stories about males breaking into houses just to get a female in heat. All they need is five minutes and you'll have a litter of kittens a few weeks later.
If she doesn't get spayed, it'll be a matter of when this happens, not if it happens.
I don't mean to scare ya, just giving my perspective on things. Best of luck.