We have 1 user that gets email on 3 devices - phone, tablet, Windows PC using Outlook

The email is coming in fine on the phone and the tablet, but in Outlook her email is coming in sporadically - sometimes it will sync normally like her phone, but then other times when she checks her phone, she realizes that she has email that isn't displaying in her Outlook - she tells it to check for mail and the mail comes in.  This has happened a few times and it eventually goes back to normal, but is there something we could do to fix it for good?  This one user has had this problem several times and no other users have.