blocking a friend from seeing a single friend as a friend

This may sound confusing, but I'll explain the best I can. One person ( not a friend on fb) shows we have 8 friends in common. When I click to see the 8 friends, only 6 are visible. Hmmm.... Then on her public part of her profile, she tagged a mutual friend that was not part of the 6 friends that showed up. That other friends friend list is only set to mutual so I can't see their friendship. . My question is, how do you go about and block specific people from others seeing it on your timeline and not everyone else? I should add he add she do not have me blocked since I can access both profiles.