if thats her in your avatar, she is gorgeous
Ok, I'm assuming your a girl?? It may be she is comfortable with your b/f because he is male and that she has spent her first 4 months with a male caretaker..
Following you around is a GOOD thing
taking her on walks = GOOD THING, I think you most likely are going to have to give it more time..
Some things I would do, is obviously if she bolts from you, don't go after her, let her go..sit ON the floor with her ALOT, toss the treats, try to engage her in some play, affection,,etc..get down to her level.. Never use a harsh voice with her, keep everything low key and a happy tone. No fast moves.
I would also start hand feeding her , her meals. this can help with 'bonding'..
To me, it sounds like she just hasn't been around a woman , is more comfortable with a man, but give it time, while she's afraid, I don't think I'd take it personally, hopefully she'll come around (which it sounds like she is, following you, sleeping with you, etc) it's just gonna take some time