Originally Posted by dreadnatty08
Do you have a custom recovery installed like Clockwork Mod or TWRP? If so you can do a factory reset in there. If not, to flash the former, download ROM Manager (you don't need the paid version); for the latter, GooManager.
Factory resets from these recoveries won't wipe your SD Card, so if you want to remove any media files, transfer those over manually and then delete. After a factory reset, you'll be prompted to enter in the new Google account and she'll be all set.
If rooted theres an even easier way. Just delete the accounts.db file located in the data/system folder.
Deletes all accounts on the phone.
Can also be located in data/system/users. Just do a search with a file explorer. There's only 1 accounts.db file on the phone so theres no confusion on which one to delete. Enjoy
If your not rooted you will have to downgrade and then upgrade again. Guides can be found in the All Things Root Guide.