Has she gone back into her account to verify that her email address has changed and that it is not the same as it was before?
If it hasn't changed then perhaps she forgot to click on "Save".
I have an email address query of my own, and this is as good a place to put it as any.
I haven't tried tinkering but my reading of the situation is that while Display Names can be set per Group, a person can only have one email address covering all their transactions with different Groups. I have based this belief on the fact that an email address is edited from "Account" accessed from the drop down menu from a member's name at the right hand side of the top bar, which implies that it is Groups.io wide, not per Group.
Is that belief correct or not?