How about the New Forest ? You can hire bikes at Brockenhurst, Lyndhurst & Burley, it's nice and flat so she won't get pissed off with having to push her bike uphill if she doesn't ride regularly. Lymington is nice and touristy with some good resturants/hotels and Burley is quaint and picuresque with wild ponies and donkeus all over the shop.
Cattle grids are a pain in the bum (sometimes literally) when cycling in the New Forest, though. Hence most of my longer jaunts tend to take me either east or north-west of Winchester.
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