For me, pushy evangelism is an irritant. Perhaps you feel the same way. (I still have a JW wife and devout in-laws who don't know when to quit.) I know Pentecostals around here that are almost as bad as JWs are toward XJWs. They use up every ounce of respect I have for them as people with feelings and push me into choosing between speaking out and being deferential, which I don't appreciate.
Did you have bad experiences with JWs harassing you after you left, or were you DFed? If you left as I did and were harassed, if she knows about your experiences, maybe you could tell her how being pushed about going to someone's place of worship makes you feel and point out how similar these experiences are. She might get it immediately and leave you alone. Unless she's feeling pressure at her church to reel you in, that is.
If your past doesn't line up with this approach, you can still explain it all to her. Tell her you--like most people--don't like being aggressively proselytized to and that this is something that's putting a strain on your relationship. Tell her you don't want to be forced into choosing someone else's religion all over again (perhaps you weren't allowed to choose the WTS if you grew up a JW?) and that, while you're glad she's getting something from her church, you have no plans to convert to anything at this time. And it may never happen. Ask her to respect your feelings and let that decision remain with you. Tell her you don't hate God or religion per se, but this isn't the time.
Consider this: it might all be a social thing. She may want you to go so she can introduce you to her church members. But if your Pentecostal's there are anything like those here, I'm sure you'll get 500 invites to come back. Some more aggressive than others. :-( If you go and this happens, share that experience with her so she'll understand that it wasn't so pleasant for you and why. Maybe THEN she'll back off. Or at least you'll find out what her true motives are from her reaction.