I have a pitbull and they told me that we should expect her to get her first period when she is 7 months old, not sure if it's like that for every dog but if it is looks like you got a month to go! Hope it helped some...
It's usually about 6-9 months. Sometimes I think it can be later with certain breeds of dogs (could be the larger breeds...I can't remember exactly)
It could be any time, so make certain she is supervised at all times. It doesn't take long for a pair of dogs to hook up and make babies. Matter of fact, a friend of mine had to be out of the country for 6 weeks and boaded her female rottie with the breeder. Her rottie was 7 months old at the time. My friend comes home, the dog seems fine but within a few weeks it was clear that her dog was pregnant. You can imagine the confrontation! The breeder grudgingly admitted that the two dogs hooked up between the chain link fence that separated them. He "thought" there wasn't enough time for conception to occur, so he never told my friend what happened.
The saddest part of this story is that my friend never wanted her dog to reproduce because she had severe aggression issues and didn't want that trait passed on in the breed. Due to work demands, and simple bad luck, there was no time to have her rottie spayed before being called out of the country. When the puppies were born, the rottie refused to recognize them and refused to feed them. Despite all efforts to get her to bond with the pups, she killed two of them within 24 hours of their birth. My friend had to hand-raise the remaining pups herself, and refused to adopt them out until they were old enough to be altered. She kept one of the female pups who was exactly like the mother - major behavioral issues that could make her a dangerous dogs in inexperienced hands. I so admire her for taking the time, effort and money to do the right thing not only for the dogs but for the breed in general and the public at large.
These are the kinds of issues you need to be aware of in case a Romeo finds your Juliet. ;-) There is no way to determine exactly when her first heat will begin, so being vigilant now is the best thing you can do until you can have her spayed.
The first heat cycle usually happens between 6-12 months old.Toy breeds usually become sexually mature sooner than large breeds.Even though they have reached sexually maturity.They still are not pyhsically mature that developes later.Females usually shows signs of coming into heat when there vaginal area starts getting swollen.Each animal is different and it is hard to say when one will come in.By getting her spayed you are cutting down the chances for her developing alot of different health problems on down the road.Good Luck and Take Care.