Assuming your wife would not find them too difficult, what about ferries? They are usually easy to get on and off and comfortable to travel on.
One leaves Desanzano at 1415 arriving Limone 1612. Not sure how close the station/ferry terminal are to one another in Desanzano but over the summer, travelling by boat is usually much more comfortable then by bus and worth the little extra.
GESTIONE GOVERNATIVA NAVIGAZIONE LAGHI - LAGO di GARDA - Orari
Good luck - lake garda is lovely.