I think there are a couple of elements here that should get your attention:

Is this more about the trip, or more about the relationship?

She sounds like a remarkably adaptable partner with a real appreciation of the outdoors. That's great. Is she ready for this trip? You WILL NOT KNOW until she goes on it with you. And when she does...are you going to allow your concern for her, and her well-being, sidetrack you from completing the trip?

Or is the trip more important to you than she is?

If this were the woman of my dreams, and she wanted to do this, I would agree--knowing that there is every chance we may have to bail early for some reason. And that would be OK. There is always next year for the rest of the trip.

If she is not the woman of my dreams, I would not want to take her on this trip. No way. Thank you very much. Way too many issues here, and too many things that can go wrong.

And if she is the woman of my dreams, I sure don't want to set up a scenario where I give her a series of goals and tests she has to meet, or feel that she has failed.

That is NOT the right way to develop a healthy relationship.

Then again, that may be exactly what she is doing to you---and you are failing! grin