You don't give a budget, but as 51 year old mum, here's what would be on my ideal list:
-ebook reader
-Nintendo DS
-tickets to a gig/show
-an antique (and I don't mean your dad) - these are good because they're unique and there's something to suit every budget.
-iPad/iPhone
-one those make-up and photo sessions that make you look like a hollywood star
-a musical instrument to take up
-golf clubs/camera/paints etc., something to spark off a new hobby or get back to an old one.
Failing which, ask her best mate/partner/sibling if there's anything they know whe really wants or likes.