Let me explain the heat cycle to you. Female Dogs go into heat at any time between 6-12 months usually. The average heat cycle for a dog is approximately 3 weeks but for some dogs it is longer and for others it is shorter. Some as short as 10 days and some as long as 4 weeks or more. Usually your dog will go into heat every 6-7 months though again each dog is different and can go back into heat as early as 4 months or not for 12 months. Most however are average.
During the first part of a dogs heat period you will notice swelling of the vulva, possibly an increase in urination and bleeding. If there are male dogs around you will notice them hanging around her. This stage generally last about 7 days and she will not allow males to mate with her during this period The second part of the heat cycle is when she will accept a male and breed. Usually bleeding has stopped or become straw colored at this point. This can last from 4 to 21 days though the average is 7 days.
Then during the last stage of heat she will be less willing to breed as she is going out of heat. This stage can again last from 4 to 21 days as well but averages 7 days.
Each dog is different so some evaluation by the owner is necessary. The whole heat period should be approximately 21 days but as stated can be longer or shorter depending on the dog.
Here is an excellent website with pictures to illustrate a female in different stages of heat.
If she should still get pregnant, most likely everything will be OK and the puppies will be born normally and your female will care for them and have enough milk to feed them and be the perfect mommy. However, since she would not mature in body and mind, you will need to be prepared in case this doesn't happen.
You will need to know IN ADVANCE how to help free the puppy from the sac, cut the cord, clean the pup and clear it's throat. You will need to have milk replacer, bottles, a food scale and other items needed to raise orphan puppies ready just in case your female has problems or just refuses to take care of the puppies or doesn't get milk in.
It's not that dogs this young can't have puppies and have everything work out fine, it is just more likely that some problem will occur so you will need to know all about whelping and arrange to have time to care for the litter if mom doesn't take care of them.
I hope you find this information helpful.