If she isn't spayed, pyometra is a very real (and potentially deadly) reality! It stands for infected uterus, and if she isn't spayed she can go downhill very fast. Also not spaying her can set her up for cancers of her reproductive system, mammary tumors etc. The more heats a cat endures, the more chances she could end up with problems like these down the road. If she has vaginal discharge it could mean she has 'open pyometra' which is better than 'closed pyo' where toxins and infection build up very fast. Cats normally don't have periods or bloody discharge like dogs do when in heat. I'd have her checked over, and spayed to avoid problems.