....By the way, it is perfectly normal for the male and female dogs to get stuck together when mating. That is Nature's way of ensuring the female gets pregnant.
This is Nature. They are both at an age able to breed. After 2 'heat cycles' she is more than ready.
I hope you are ready for the pregnancy, and the pups? Her pregnancy will last about 8-9 weeks. She will most likely be fine even though she is young. But you may need the vet here and there, and you will have to keep a good eye on her. It might not be an easy birth when the time arrives, because he is so much larger than her. The pups could be too big to pass through the birth canal. That could be when you will definitely need the vet, so be prepared.
After the birth, do consider having her spayed. Otherwise this could happen again (probably will!) and it will put too much strain on her to be continually breeding. That could considerably shorten her life.
Update us PLEASE! I'm a softy for pups!