i tried to invite an external user into our sharepoint environment, but she keeps getting an error. "the invitation cant' be accepted right now"

i figured out that an account with that address was already in our system once. but i removed that one, , it's no longer in the 'all persons' userlist.
i've tried looking at the web version of the userlist, i've tried the powershell command (spo get-user) .. the account isn't there...

however, if i press share, it still pops up in the autocomplete function.. which leads me to believe it's still somewhere in the system...
if i do a search, her name also pops up in the list of persons, but when i click the name, it just points to an error page (can't find that person)

so, how do i completely remove this account if it isn't in any userlist? it seems that she can't accept any new invitations as long as the old one still exists, even though it's nowhere to be found...
[personal information modified by msft]