Once a cat goes into heat, she becomes very uncomfortable.  She could continue to go into heat about every two weeks until she becomes pregnant, if nothing is done.  She will cry and try to get outside, with every fiber of her being.  This is why, if you don’t want kittens, you should have your cat spay.   If you take her to the vet for shots to help with the discomfort, it will return when she comes back into heat within fourteen days or so.  There is no reason for any animal to suffer in this way.  I hope you will get her spay and end her suffering.