Get her to check she has not blocked your domain or email address.
She needs to log onto her BTMail account using a browser, not an email client/app, and then click on her username at the right hand side. Select "Settings" then go to the left hand side and select "Mail". Scroll down and click on "Blocked Senders".
Scroll down the list until she finds either your email domain or your email address or both. She should then click on them and select "delete".
While she is in the settings she should also add your domain to her "Safe Senders" list which she will find in the list above the "Blocked Senders".
