Neighbors

When we first moved into our duplex, our upstairs neighbors were awesome. We hardly knew they were there except for the occasional run in outside, or the kitty paws pattering on the floor when it decided to run around like crazy. But even that you wouldn't usually notice. They were super nice every time I saw them.
They moved out at the end of May.
Our new neighbors... well... the guy is nice.
I'm trying so hard not to make judgments on the girl. They are probably my age. Maybe even younger.
Lets just say she did not make a good first impression. She acted bitchy and rude and stuck up the two times that I have seen her. I say it that way because we have never talked. The first time, she completely ignored me as I said hi, and her boyfriend responded. She interrupted him. And the second time, well, I think she may have said hi, but it could have also been to the person she was on the phone with, who was severely yelled at a few minutes later.
OK. So she may be really stressed about moving. She wouldn't be the first person to act a little crazy because of that. Or maybe she was having a bad day. Twice.
I am just worried because I CANNOT deal with neighbors even a fraction as bad as the ones at the old apartment. They made me hate my life. I couldn't sleep because they were always yelling or banging on the floor or something. Basically, we just couldn't live like that. And I don['t want to be reminded of them, or worse, have to deal with people like them again.
I know that I am getting a little preemptively angry here, but I am just worried.