i'm not sure if its possible, but i've had issues with upgrades in general (even from 10.5 to 10.6), so i'd suggest a clean install of SL.
back up her drive, fresh install of SL, then migrate.
my magsafe adapter doesn't necessarily get hot. i just checked and i wouldn't be able to tell its charging right now (amber light)
i'm guessing you tried another outlet? maybe take a closer look at the connection between the mbp and charger.