how do u make your profile invisable on fb?

[princess monika]

the other day a girl who is a friend of a friend on my facebook became completely invisible and i thought she had deleted her self completely of my page. then the next few days she reappeared as my friend again without me having to add her again, she had been on my friends list the whole time and she" fb is never private goes to show u". so now i think she still on my page lurking as invisable. but i havent got a chance to ask cause shes always invisable where i completely dont see any profile info at all (ex.name,profile pic) does anyone have any idea on how this is done???