I think this could be a definite possibility:::
She is a senior in high school, right? So she is definilty old enough to have a boyfriend. I think she called to "make sure" her father was on his way to New Jersey already so that she could have someone in the house who normally wasn't allowed in the home. I am thinking a boyfriend or even if she was possibly gay, a girlfriend. Perhaps she was going to have this person over to have sex or to just spend the night with them, or perhaps she was about to break up with someone. But if that were the case, if she was about to break it off, I don't see why she would call to make sure her dad was on his way out of the state. I think it's more likely that she was having a boyfriend or girlfriend over for some time alone together kind of a thing. Now the question to me is this, is it possible that she recentally broke it off with someone else? Maybe this person wanted her back? I think she was waiting for the person she wanted to spend time with, and the old person, an old boyfriend or old girlfriend shows up at the house. Her dad said you can see outside to the porch to see who is there. So she hears a knock or the doorbell rings, she hangs up with the last person she spoke to, she sees it is her ex out there, and she lets them into the home, figuring they just want her back and she will be as nice as possible and explain to this person it is over. They come in she tries to be nice about it, it doesn't work. Maybe she's even hurrying them along because she is expecting someone else over the house, so she ends up being a little bit curt with them and it doesn't sit well with whoever is over there and they end up in a fight. It escalates and they end up screaming in the kitchen. WHo knows who picked up the knife first, but either way the other person ends up stabbing Holly and not the other way around. If this was someone she was dating, I am sure he or she has been in the home before and knows their way to the bathroom, etc. And putting the phone off the hook, almost seems to me like someone wants her to be found. If you take the phone off the hook and people get a busy signal for a long time, they are more apt to check on the person than if the phone just keeps ringing. Ringing usually means someone is out. A busy signal consistently for a day or so usually means something is wrong. Just some thoughts.