Standard account: keeps losing Windows mail profile and background

I'm using Vista Home Premium.I've set up standard user accounts for my wife
and daughter. All has been well for several weeks and all of a sudden my
wife's account keeps losing its settings: The background wallpaper keeps
reverting to the default (a minor cosmetic problem); more importantly Windows
Mail disappears (and with it her email inbox). No problems with my daughter's
account or mine for that matter.

Any clues a) about how to retrieve her emails and b) how to stop this
happening?