Are all females who are ajnabi, ajnabi?

My question is whether all ajnabis are ajnabis ? This might seem confusing . So here's an example - I went to my friend's house and he has a daughter of about 7 years of age who has obviously no yet become baligh / attained puberty.She is obviously not mahram to me . Is it a sin if I pat her head ? Is she Ajnabi when she isn't a woman technically ?