The french fit is the starting point.my saddle is a bit higher than the inseam x .883.Depends on how your foot works on pedal.Riding with heel up or heel down or just flat will alter that formula some.You got the right idea going on.As far as your wife goes,its a risk spending more and her not riding.However better to get something she enjoys and she probably will ride it.Crappy bikes are no fun to ride. Sell mountain bike to help offset cost of her new bike.