Thanks for the replies folks.

You see, I'm trying to do it all on a budget - she's got a few other things she wants as well, so I was going to try and cover a few bases. The bike I suggested here is less than half of the price of the bike new from a shop, but if it's the wrong size there's no point.

I may have another source though - a bike auction, but I don't have much knowledge of the brands - can anyone give me a sliding scale of the main brands and how they rate? Sort of like...

Brand1>Brand2>Brand3> etc etc?