If she has backups on her local storage, she can recover the deleted chats.
Here are the steps:
- Open your phone's file manager
- Go to WhatsApp > Databases
- Find files called msgstore-YYYY-MM-DD.1.db.crypt12
- Rename the backup prior to date of deletion to msgstore.db.crypt12
- Uninstall and reinstall WhatsApp
- Restore the backup