JWs don't see the difference between the Watchtower and God because they think that the "society" (Watchtower society) is Gods mouthpiece on earth and they are the only ones who teach the "truth". This is why she denies being bothered about the watchtower and just says she is trying to serve god. For her, serving god is going back to the JWs (Watchtower) because they're the only ones with the truth.
As for sex. I hate to say this but have you considered that if she didn't have this JW dilemma (these feelings of guilt) she wouldn't actually be marrying you ? She might be wanting to get legally married JUST to be able to continue the relationship with you and have sex with you without guilt......and not because she is 100% sure of the marriage itself. Also if she is married she can go back to the hall and they will let her back in....but they would NOT let her back in if she was not married to you. Please don't be annoyed at this suggestion. I have known EX JWS who have had boyfriends and live with those boyfriends and even though they don't TRULY want to marry the guy they still talk about marrying them just so that they can be approved of by the JWs or their JW family.
So if she is faced with either leaving you or marrying you, she will pick marrying you even if she isn't really sure.
Sirona