One of the things that happens from being in heat is that it causes bloating and inflammation. This can put pressure on their bladder making it feel like they need to pee, so they try and try. Its not out of the question that she may have a UTI. You would need to bring her to a vet to test for that. Are all of her vaccinations up to date? Be sure to have cool clean water available at all times. When any of ours were in heat, they always seem to have drank more water than usual. Also, unless your planning on breeding her, you may want to consider having her fixed (spayed/neutered). Once fixed, animals have fewer behavioral problems, are less aggressive, overall have fewer health problems and live longer happier lives than those that are not (not that yours have any of these problems). Good Luck!