My boxer hasnt been in heat yet

Question
I have a 19th month old boxer and she still hasn't gone in heat yet. I was wondering if maybe she wasnt able to go into heat because where i got her. I guess her father is her brother and then a vet told me not to even breed her but i know most dogs are in red anyways to keep the true blood lines so I dont know why she owuld even be so rude plus I dont intend to breed her with a relative anyways. can you tell me why she hasnt gone in heat yet?

Answer
Is her sire her full brother? Line breeding is a good thing done correctly but that is inbreeding and not linebreeding.
it more than doubles the chances of genetic problems which can be passed on no matter whether you breed her to another relative or not.
Your vet is just trying to protect you, and your dog.
She might never come into heat. Or she might've had a silent heat and you missed her. I would vet her, have a full hormone panel done  and check to make sure she has all of her 'equipment' and that it's functioning properly. Then have her tested for all the genetic issues that plague boxers prior to breeding. That's something that should always be done, not just in her case :)
Good luck
Cindi