If she's using Photos, check the size of the Photos application. If it's amazingly large, right click on it and "Show package contents". If that app was carried forward from an original iPhotos installation, it may still have a dead iPhotos library inside it eating up a lot of space.
Of course, make a backup first, and then remove the iPhoto Library.
I also really like using
OmniDiskSweeper to help me find hidden pockets of obsolete storage in my Library folders.