Tracking log on Exchange 2013

I use command Get-MessageTrackingLog to trace mail on Edge and see mail sent to customer from Mailbox server to Edge , but when I go to Mailbox Server and trace to find mail of customer which I see when trace on edge, no result. Issue only affect to all mail of her.  I can trace and see all except her.

what does that happen?

Many Greetings and thanks for any hint.