I know you are looking for the consequences, but I believe you are asking the wrong question. Like you, I’m agnostic, however, you need to work with HER logic and perspective of the reality she has constructed. Assuming you are being intimate, that would mean that she is cheating on her God. God has set a rule which she is vehemently breaking with you. Considering that God is supposed to be more important than anything else, including you, what does that tell you about her integrity? Integrity is not a word owned by religion. It also applies in marriage. By the fact that she’s pioneering, I’d assume that she strongly believes in a large portion of the teachings and thus violating her conscience when she gets intimate with you. That shows a severe lack of respect for her core beliefs and values.
You may believe that it is not such a big deal considering various Christian denominations where sexual immorality is tolerated, but for JWs, this is a very big deal, very big deal. Her ability to be doing this, without telling anyone, all the while pioneering is very telling.
She is not in a good place at all right now. She either needs to come to terms with the fact that she is not a JW and live happily ever after with you or she needs to stop doing what she is doing with you, confess, do things right by her faith, God and Religion. These sorts of decisions/changes will require lots of work on her end and this will require lots of time.