Females go into heat approximately every 6 months. It can vary with every female. Also their first heat is after being 6 months old.
Between the 9th and 12th day after going into heat they are ready to mate. But again, every female is different. Some females can still get pregnant at 21 days after going into heat.
Are you asking this because of the girl you might get?
To avoid unplanned litters it's better to spay the female
Otherwise you will have to be very careful and keep the dogs away from each other and that's not fun for them