If she's reading the mail with OE - it's possible she's got it set to display only unread mails. Check in OE under View - Current view.
A bit more info on the mail-client/whether webmail or not - would help.
Samsung Galaxy S8 review
1995-2015: How technology has changed the world in 20 years
This 2D animation about monsters is illustrated in a Van Gogh painterly style
How to get WWDC 2017 tickets
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.