In ball pythons, in-breeding, if you don't overdo it, is not a bad thing. Sometimes it is the only way to prove out a potential new morph or to duplicate a cool one found in the wild.
Also, it usually is rule of thumb that a female should be around 1500 grams and over 2 years old before you attempt to breed her. Some do it earlier with no harmful side effects . . . they will not breed until they are ready.