I have the same problem here. My g/f thinks the great outdoors is the back yard. Here is what I did:
First off, let her know that the vehicle was in 100% operating condition. While I drive a 1973 Land Rover, I think the Jeep JK will offer the most comfort in this department (knowing that it is fairly new and the jeep brand is known as an off road vehicle). This removes the vehicle requirement unknown.
Second, go to a location already known. When my g/f asked where we were going, I said, "Oh yeah. Over to the park 2 hours away. I go there all the time." This lets her know that I know what is going on there and what to expect. Also letting her know that your vehicle has been there a number of times and is capable of handling the terrain. Once again, removing an unknown of location and equipment capabilities. Also let her know there is cell reception up there. I know this sounds stupid but having absolutely no contact can be scary to those who aren't used to it.
Your first destination should be close to your home. I would say no more than 3 hours away via car. This keeps things comfortable.
Third, I waited for fair weather. No freezing temps. Not too hot (ok it was hot but not completely miserable) and no rain. We did experience wind but we just got in the truck. Miserable weather can lead to a miserable time.
Fourth, informed her personal gear list. I literally wrote out what she needed to bring. Crap from sunglasses to whatever pills she takes to clothes. We went and got her a pair of boots (with the oversized socks, etc) and other things at REI just to make her life a little easier since nothing she owns is geared for outdoors. You have removed the "what to wear" unknown. I know this sounds stupid, but it is part of the mystery of the opposite gender. It is not to be understood, just sorted out before you hit the road.
Fifth, schedule. My g/f is obsessed with schedule. She is always super busy so planning ahead and schedule and all that crap is crucial. Weeks and weeks beforehand, she knew I was picking her up at 8am on a Saturday (more like 8:30, but I knew that) and we would return roughly around noon on Sunday. No later than dark on Sunday night. This adds structure.
Sixth, share the plan/map. She knew were she was going (later I found out she shared this with her friends and family so they could come find her body...yeah this is what I'm dealing with). Also lets her know that there are "nearby" towns and whatnots. Now she knows that it isn't that far off the beaten path (well this is typically the case on the east coast). Once again, removing unknowns.
Seventh, any of her female friends into camping and whatnot? Guess who she will and won't listen to... Yep. She won't believe a word you say (despite your experience) but her friend that went camping once in college for one night...she is Bear Friggen Grylls in her eyes. I can't tell my g/f a darn thing but her outdoorsy friend can convince my g/f to go backpack the Appalachian trail in half a sentence. Once again, another mystery of the opposite gender. Just roll with it.
Eighth, you need flushing toilets and running showers...like real bathrooms not a tarp with a water hose hanging off the side of your truck. DO NOT SCREW THIS UP. Seriously. Bite the bullet. Plan the trip to go near gas stations and crap. When you approach these waypoints, inform her this is the last flushing toilet for 6 hours (even if it isn't, say it). You'll be stopping...btw this is a great time to check out new games on your smart phone.
Ninth, good food. Now is not the time to bust out the freeze dried squirrel. Have good food. For our first trip, we had steaks and chopped potatoes on the grille. She ate very well that night and that helped.
Tenth, be prepared to do everything yourself. Despite education on tent operation, sleeping bag operation, etc, it sometimes doesn't translate immediately.
Eleventh, go to ace hardware and buy stuff that you put down on your lawn to keep bugs/mosquitoes away. When you get to camp, throw this everywhere. TRUST ME it will reduce the amount of loud screams and general complaints about bugs.
Twelfth, you know your stories about that time you were hanging off the side of the cliff in your truck? Or that time you got frostbite on your toes? Or that time you had to scare off the wolves with a torch you made out of a shirt? Yeah. KEEP THAT TO YOURSELF. While you and I think all of that is cool, to someone who doesn't know, that is scary as hell. When it is scary, it isn't helping your cause. So yeah, keep your mouth shut on that kinda stuff. However do inform her about the beauty of the surroundings or all the stars you can see at night, etc.
Thirteenth, pick easy trails. I'm talking the kind of stuff that you probably don't even need low range for. Yes, this is wuss but when you start jostling her around, it gets scary. As with #12, scary=scared away. If she looks uncomfortable with an obstacle, offer her the chance to get out. Then let her know it "isn't any big deal" (BTW don't screw up and make it a big deal). Toward the end of your journey, if see is really taking to it, offer to let her drive. A dirt road for her to drive your rig on is the perfect balance between keeping it exciting for her as well as keeping it under your control (I've seen g/fs run trucks off the road before, once again, this doesn't help your situation).
Lastly, try to go with others that also have wifes/girlfriends that do this as well. Once again, any word that comes out of your mouth is null and void but if it comes from another woman that yours just met, its solid gold advice. I noticed this when we went with a bunch of other friends camping late last year (totally needed Morgan Freeman to narrate how all the men gather around the campfire drinking beer while the women went off and did...whatever it is they do). She was complaining about all this crap there but after she talked to the other womenfolk, no more issues and she was totally on board. She had a lot of questions and the other gals were able to fill her in. Their communication was received better than mine and stuck.
Is it a pain? Yes. However I've done the "throw them to the wolves" kinda deal and that NEVER works. As you can tell, I met all kinds of resistance getting her out there. However once out there it was ok and I think she had a pretty good time. It gets easier each time you go and keep easing into it. Don't do an easy trip the first time then a 10 day self sufficient trip the next time. She knows what to expect and she can be more proactive. We still aren't to the "no running water" thing but that will take time to ease into it. I'm doing it in this fashion because if she isn't 100% on board with this, then it will go sour REAL quick and she won't have any part of it.
So yeah, that is what I'm doing with my girlfriend. Easing her into it. No surprises. No scares. No misery. Its going to take time for her to accept it. She isn't very excited about I'm going with "comfortable" for future trips that require camping.
