If you trust someone enough to get intimate, then you should trust them enough to not do something stupid with your firearm. If you're the kind who has sex with someone you just met and dated once or twice, then you're already risk-tolerant. Having a firearm is just one more of the many risks you accept.
If I were ever in that situation, and we are in a hotel/motel, there is likely a safe in the room assuming you aren't in some seedy motel.
It's not hard to wrap your gun in your clothes while she's not looking to keep it from view. You could also slide it in a dresser drawer while she's using the facilities.
If you are at her place, there ought to be placed in the bathroom that can hide a gun -- linen closet, under the sink -- places most people don't look often. Or again, just fold your clothes around it and place it on the side of the vanity/sink or on a chair.
If you're really worried about her politics, let her see it when you're dressing. That way the evening wasn't ruined, and you'll know whether she's someone you want to see again. Same thing for her -- if the gun is a deal-breaker for her, she now can make an informed decision.
If nothing else, letting her see you carrying is a good way to approach the subject so you can talk about it. If she's curious or triggered, she'll say something.