I would suggest that she sets up an account on an e-mail client and downloads all of the e-mails on to her computer and off the BT server. She should then archive them or drag them to the googlemail account on her system.
Another little gem is, in settings, accounts and import, under 'check mail using POP3', click on 'add POP3 email account' and add the account. You'll receive new emails via Google mail from the old account. Still in accounts and import select, in 'send emails as'; " Reply from the same address the message was sent to", if needed.