You’re both new to MTBing, there’s no such thing as being a sh’t rider, we were all in your/her position once … fitness and ability will develop with experience … be as patient and encouraging as possible, and just enjoy being out on the bike
tips on how best to build hill fitness
unfortunately, the only way to improve hill-climbing is by hill-climbing … but also, as MartinGT implies, being in the correct gear makes all the difference … i.e. are her climbing troubles due to technique or fitness?
For ‘easier’ rides to get fitter and more confident, try the trail centre at Llandegla
(maybe slightly more than an hours drive though). Not too technical, nice fast flowy trails, a few decent hills on the Black run, and a superb post-ride cafe & bike wash.
Or there’s the Peak District – I’d suggest starting with routes around Hope or Ladybower Reservoir at first … then if you want more challenging climbing aim for Edale, Jacobs Ladder, Hayfield, Mount Famine, Rushup Edge, Mam Tor …
Or for something a bit different, try Lee Quarry & Cragg Quarry (nr Bacup) … kind of like a trail centre, more compact, more technical, not so much in the way of climbing