Combining FOREVER accounts

I have run into this issue several times where clients mistakenly create more than one account and then unfortunately purchase something in each account.  I would love to be able to combine accounts into one when this happens - even if it means losing the 2gb of data from one of them.  My most recent incident was made more complicated by the fact that she has storage in her first account and that email address is being discontinued by the host organization.  However, she accidentally created a new account with her GOOD email AND just bought a box on it.  We can easily gift the box to her other account but now she can't update the email on that original account because it is being used.  She really doesn't want to create a new email just for us.  Why is this such a problem?