no more puppies?

Question
We have a female "mutt" dog. She had puppies about nine months ago and we did not get her spayed. We was concerned as to why she hasn't come into heat again. We are glad that she hasn't but when or if she does we want to take her to be spayed so we don't have any more unwanted pups. So this is my question: Could there of been something internally wrong with her as to why she hasn't come in heat or does it just take a while? And if it takes a while, how long?

Answer
Hey Tonya. Dogs go into heat about twice a year. You need to have her spayed before she goes into heat again though. If you wait until she goes into heat to have her spayed, then the cost will be much higher. Just b/c it's a more involved procedure then. Sounds like she's going to come into heat before too long, so I would get the spay done pretty soon. Thanks!