Based on the available information on the abilities of the "Guest" account , it cannot do much except receive calls and use some of the available Apps. Deleting anything should not be possible.
The users feature lets you share your device with others while keeping your personal or work information private. For
example, users that you add to your device can't access your info, such as your email, contacts, pictures, apps, and more.
By default, your device is set up with a device owner and a guest.
You control whether the user can use the phone app to make and receive calls and whether the user can send and receive
text messages (SMS).
Bottom line is you control what the guest account can do and cannot do.
The link below offers more details.