I am a walker and I might put that in on an average week. I've hiked twice that and more in a day but that is not the same. I'd have to be pretty hard pressed and this would have to be some special friend for me to make a 10hr return journey.

If this friend then is so special, why are they not picking you up? What is that, a 40 min drive (sorry, can't visualise miles)? I have driven that every day to commute. It seems relatively no bother to me; and, if she values your friendship, it ought not to to her. I have regularly driven that kind of time across a large city to have coffee with a friend and thought nothing of it.

That being said, what are you offering in return. Common etiquette would have you giving her some money for gas.