Its the first time for her to get pregnant and she is 1 year and a month old , she mated with the same cat about three times , she is a medium size cat , so how many kittens could she possibly give birth to?
It's very hard to predict. It depends how many eggs are released and fertilized. and they release multiple eggs at once. It's not some direct relation to how many times she mated. Then it depends on the health & viability of the embryos. The average litter size is 4 to 6 but it could be anything from 1 to 8, and occasionally they have more. I heard of a cat having 12!!! That would be very unusual though. Two isn't unusual, but neither is seven. One of my cats was one of a litter of seven. It was his mom's first litter, at 12 months old, and she is a Siamese girl about 7-8 pounds. If the mother is very young like under 8 months then they do tend to more often have smaller litters ( they are also at bigger risk for complications , so it's better they don;'t have kittens at all that young. ) Also a very small cat like 5 pounds will tend to have a small litter. but otherwise , it's anyone's guess.
Thanks for putting where you live in your profile.
3-6 is typical but as said above, can be anything from 1-8. A friend's maiden Siamese queen had 7, another friends maiden BSH had 6, my own cat 20 years ago had 3. The various cats I've foster have had from 3 to 6 kittens.