My girlfriend likes to be kissed on the neck.
Does it seem unusual to you that she likes being kissed on the neck?
No not really, I've had other girlfriends that like to be kissed there as well.
It is wise to know what her boundaries are before doing something so intimate as to kiss her on the neck. That can lead to bad reactions on her part.
I prefer that she tells me what she likes so I don't offend her.
It's good that you respect your girlfriend enough to know what she likes and doesn't like. It good to have a relationship built on mutual trust and respect.