BSH's or cats in general have different personalities, and no matter how well you select when you breed there will be cats that aren't as social as you'd like them to be. I have had 3 BSH and all of them had different temperments...I visit breeders and they will have cats that greet you and the door and cats that are under the couch..
If I were you, I'd back off from forcing contact. I'd maybe pick some special treat or snack that she really likes and then begin there...teach her that you're good for her. Sit down on the floor and talk to her while you give her treats. after a while she'll learn that being with you comes with a reward. Once the trust is established you can go from there, and just sit down and talk and she'll come...it takes patience and lots and lots of positive re-enforcement.
Has she always been this way?
When you visited her as a kitten at the breeder, what was her temperment then?
Is she spayed?
Has the vet made sure she is healthy?
Does she eat, drink and use the potty normally?
Does she have a feline friend?

There are soo many factors playing in when it comes to behaviour, and it can be hard to really give you a definitive answer.

I adopted a 2 year old british boy. He was SO shy and it took me about 10 days to even get to touch him. He had been living with a single lady that was never home. He has SO anti social it's not even funny. With lots of hard work, and patience he is now (at the age of 5) the nicest cat - to me! He tolerates my guests but he wont allow them to go near him, and I always ask people to ignore him because it's too much for him. IF they disrespect his wishes and touch him anyway they will recieve a smack with claws. He likes very few people, but he absolutely trusts me, and would never in any way hurt me.

I wish you all the best with your girl and will be looking forward to your answers.

take care