Female here...with a boyfriend who LOVES off-roading and camping. I'm willing to go (I like adventure, travel, and camping too), but these have been issues for me at various times:
1. Heat - I HATE being hot. I'm not fun to be around when I'm hot. Take me on a trip in the spring or fall - even winter - and I'd be happy.
2. Too much driving - I hate being in the car. Why do I want to drive 6 hours to arrive somewhere in the middle of the night...just to get up early to drive all day and the next...and then drive 6 more hours home?
3. My schedule - I was working 12 hour days as a teacher (yes, I was usually at school 12 hours a day) and he'd want to go on a weekend trip that required 6 hours of driving each way. I couldn't even fathom it being fun because all I could think of was how exhausted I'd be on Monday.
4. The company - trips with people I know are far more appealing
Here's the deal. If off-roading/camping/whatever is not her thing (i.e. she wouldn't do it if it weren't for you) and you want her to be there, you should do everything in your power to make her comfortable. My BF did this when he wanted me to go shooting with him. He arranged for people to help make me feel comfortable (I had never shot before), he got a gun he knew would be easy for me to use, we went on a chilly fall day (hallelujah!), he didn't make me do the planning or the work, he worked it around my work schedule, etc. And I had a good time! I'd even go again.
He's yet to follow that plan with off-roading, but maybe someday!