.htaccess: blocking web addresses

[Donna]

ok me and my cousin have done so much searching, but we can't figure how to block a webaddress from viewing her site.

there are only 2 sites that she doesnt want for them to view and its for direct linking purposes =\ she only wants those 2 blocked and everything else can have access to her site.

we've already tried so many codes, but we can still see her directory on this one person's site =\

thanks in advanced! ^_^