Could try one of the Uni clubs? A friend is 'cycling co-ordinator' of the High Peaks Club at Sheffield (proper) Uni. They've got all abilities and would probably be up for taking someone else riding. Try Matt on email@example.com
Mrs Soulwood is interested in joining a group or club of like minded people for mtb'ing in Sheffield. Doesn't have to be an all female club, just one that doesn't drop you at the first climb….She describes herself as an intermediate/middling rider, but needs to get rid of some of her "Mum-ness" and descend and negotiate tricky stuff well.