When we got back from our hols (UK) my daughter asked why we had not answered any of emails, as we hadn't received any we started to investigate and found they had all gone into junk mail, and that is what has been happening ever since, no one else's only hers. My husband has spent hours trying to find the reason why but is getting nowhere, would appreciate any help you can give.
Is she in your contact list, or is her email address there up to date?
Email clients usually let those through.
I do not use BTInternet mail, but there is usually a button to mark as 'Not Junk'.
Also, just dragging the emails from the Junk folder to your InBox might indicate to future emails to go to there.