Unread emails still showing on iphone 6

Since updating my mums iPhone 6 to ios8 , her mailbox is still showing unread messages. I have got her to go through her emails and folders and delete all old and unwanted emails yet it is still showing unread emails.

I then decided to delete her email account off her phone and iPad and then set them up back up which seem to have solved the problem for a few days. But her inbox is now showing unread messages again . Can anyone help please !