If the update was over the air (IOW, she received a notice that there was an update and she accepted it), whoever sent the update (her carrier or Google) is responsible for restoring the phone. The law sees it as "you broke it, you fix it". Have her bring the phone to her carrier to determine whether they sent the update or not and, if Google did, whether the carrier will make good on it or she'll have to contact Google. (She may have to take it to a different store of the carrier's - not all stores do repairs or replacements. A full reflash will probably fix the phone. But whatever is done, any data on the phone will probably be gone, so I hope she's the kind who does regular updates.)