And I son't want to sound wholly unsympathetic to your situation. It wasn't entirely clear from your OP what understanding you had with your friend when you first decide to do the ride our how clear the expectations were. From the sound of it, you've tried to address the issue and offered some solutions. If she's not interested in trying and isn't even having fun, then this sounds like her problem, bot yours. While it would ideal I'd you could sort it out without much drama, that might not be possible. There's only so much you can do for someone who's seemingly more interested in complaining. Perhaps it's time to cut her loose (in terms of the ride)--with the proviso that if she decides to really get on board with training, then you're there for her. If she's not, then you'd like to spend time together in some other fashion.

Good luck and kudos for the progress you've made in getting back in shape.