It appears that her mother's profile (which was created by a now-closed WikiTree account) is an orphan.
If a profile manager is unresponsive, their account may be closed. If that happens, open profiles for which they are the sole manager will be orphaned, and privacy-protected profiles for which they are the sole manager will likely be deleted.
If that's what happened, it's possible that your grandmother's profile was managed by the same PM and was privacy-protected. If so, your grandmother's profile may have been deleted.