What factors in Julia's personality make her attitude different?any specific events pertaining to the text are welcomed.

I think that one of the underlying intentions of Orwell,
despite the harshness of the overall tone of the novel, is that he intends to assert
that there are 'higher' or 'deeper' instincts and drives in the human spirit. Even
though Julia is seemingly a product and a victim, her spirit drives her to somehow
maintain something genuinely human and sensitive, even if it is her 'sub' or unconscious
response to do what she does. She is to the Party, subversive, in that she is also a
member of one of the Party's tools that strives to supress anything that is genuinely
human and sensitive, as it poses a threat to their power. By sleeping with party
members, she also serves to illustrate the falsity and prententiousness of those who try
to control others for their own sake of maintaining power and control over the masses
while not 'practicing what they preach'.  Her liasons with Winston are not just for
sexual contact. They talk, listen, share food, and so on. One may say that possibly
Orwell shows that there is a 'chemistry' between the two that they were drawn to because
of some remnant or intuitve sense of 'goodness' that is still there, even though they
will never recognize it as such, amidst the brutally controlled and maintained political
and social (so called) order.