Your friend has probably created a “managed user” account for his wife.
However, managed users don’t get access to any other servers than their “owner’s” one.
If they both shall have access to your server, they must both use “full” plex.tv accounts.
But if they do that, they face another issue: if not at least one of them has a Plex Pass, they cannot use Fast User Switching to quickly change the user account on a shared playback device (e.g. the TV in the living room).
I suppose that might be convenient for some but it’ll also mean everybody will be able to share and re-share your media and finally complete strangers accessing your server. It seems to me, this will also move Plex beyond any grey area of file sharing, so I guess it’s very unlikely this is ever going to happen.
That being said… there’s existing feature suggestions asking to allow sharing with an entire Plex Home or members of a Plex Home automatically getting access to what’s shared with the Plex Home admin.