LOL dude, I've been in this exact situation. Working with horses for someone who didn't know anything, and I didn't know much more than what they did at the time. Is becoming a horseman/horse trainer your goal? If so, you'll get a lot of experience out of this deal but I wouldn't count on changing the owner much if at all. Even if you fixed the horse for them they'd just ruin it the next day anyway. Not that you shouldn't do it. The more horses you handle the better you'll get.
With the catching, another possibility is that by walking after her for an hour the main thing you're teaching her is to walk away from you. The position of your body and the direction of your energy and attention in relation to hers are the key factors in catching horses. If you don't know where you're supposed to move and when, you'll actually teach the horse to become worse instead of better. If you want to gain the skills, you've got to start studying hard and figuring out where you're going wrong because this mare is quite a handful. XD