At least she has been honest with you, up to this point. If you continue, you will be pressured to convert...subtly, slowly, but surely. Dinner with her Theocratic family, where the main topics of conversation are Watchtower related: the meeting, going out in service, who is DF'ed, who was selected to go to Gilead (missionary school) or Bethel (headquarters), who will be the next ministerial servant, etc. Or you may be asked to go with her to a meeting "just to see what it's like" or to hear her cousin's first talk, or be invited to attend their "memorial" (of the Last Supper, this is the only annual JW holy day.) An elder may "just happen" to drop by and engage you in religious conversation. Most of all, if you are not a JW (or at least a potential convert) then you are not Acceptable Husband Material, and therefore not to be dated (JWs`are supposed to date only with serious intent to seek a spouse).
She said we cannot be boyfriend-girlfriend cause she is a JW.
The implication of this statement is that you have a choice to make, because she and the Watchtower religion are a package deal. If you continue to pursue her after she said this, it will be seen as an openness to Watchtower conversion. It is important that you understand that this is the way the Witnesses see the situation!