I couldn't see any way to change the email address of a site member, so I removed them as a member, expecting that I could make them a member again but with the correct email address, but they still show in the list with the old email address without an "invite" button.
Looks like it just took a while to register the removal of the name from the site. I went back later and the email address was gone and the "Invite" button was back so I rejoined her with her new address.