The injection is called Delvosteron, and will prevent her comin into season if given just before you think she is due in, even if she actually starts her season you can still give it.
If you don't want a bitch to be spayed you can give this injection to stop them coming into season until you decide to stop it. After the first injection, the second one is given after three months, then after four months, then five months and every five months after that. Greyhound bitches are frequently given it so they can keep on racing, as they have to be off the track for 3 months when they have a season. I use it on two of my bitches, as we have an eye problem in our breed which is being researched, and I don't want to breed from them until a DNA test is found.
It can also be used to stop phantom pregnancies.