I'm trying to get to grips with what you are explaining. You should be able to sign in to the service provider who is hosting her web site and change the redirection on to whichever service provider you wish.
I suspect that if you close your Virgin account you'll loose your email account, like you do in NTL.
Is there a reason why her emails are not using the pop3 like pop.companyname.co.uk and outgoing smtp.companyname.co.uk. and using OE? If the reason is for web mail access from anywhere, then it might be worth considering one of the free web services like Lycos or Yahoo to redirect to, you haven't mentioned the ISP you thinking of for BB, if its NTL they do have web mail access like most of them have.
Just one last question, have you checked if the service provider who hosts her web address allow web access to emails? Most do.
I'm not sue if I'm reading this correctly, so please explain if I'm not.