she must have at first been sick to her stomach with panic and fear and wondering what to do. She had a situation on her hands that was out of her control and she knew she had to have help handling this. That explains the fast and furious flurry of calls to her parents that occurred that Monday afternoon. When they didn't answer their phones that gave her a few minutes to think and if you were her what would be the first thing that would have crossed your mind? "What is Mom going to say?" The one person in the world whose opinion of you, you most care about. That's the one confrontation you are going to dread the most and probably the one you're going to want to avoid at all costs. It's too late to avoid it now, but you want to postpone it as long as possible - you do though, want to know when Mom finds out because you don't want that coming down on you without any kind of warning. You want to know when the body is found so where are you going to put it? You're going to put where you can keep an eye on it and know when the jig is up. You're going to bury it in the backyard so you can know if someone has been close to it or messing around by or in it.
You look at the body for awhile and you start to think that she's dead and nothing is going to bring her back and you didn't mean to do it and when it is found out your life is over anyway so why not try to buy some time until you can think what to do. So you get a garbage bag from the kitchen or a duffel bag from the bedroom and you put the body in it and you get a shovel and you bury the body in the backyard. That way you'll know right away if it is found and at the same time you think it doesn't look that bad if you do it that way rather than dump it in a swamp or river. Then you leave and drive around all day sick to your stomach with fear and trying to figure out a believable story. You can't stand it though and you keep calling Mom and then Dad to see if anything has been found or if they're suspicious. That explains the second flurry of phone calls you make that day.
When nothing happens that day and nothing happens the next day or the day after that you begin to think that maybe it's not going to be found and by staying away you can avoid confrontations or suspicions. When you get away with it for awhile and life seems in someways easier without a kid you begin thinking that maybe you better move the body someplace where it can never be found. So you dig it up, you put it in the trunk of the car and then drive someplace you think is safe from anyone seeing you. But there isn't really any kind of place like that, that you can think of anyway, you try some places but everytime someone is around or driving down the road or you see lights coming towards you, so you make the decision to wait awhile and come up with a better plan. In the meantime you're forced to leave the body in the trunk of the car which in a way is a lot safer because you always have the car with you.
But then the car begins to stink and it gets worse and worse and you begin to worry that maybe someone else is going to smell it or has smelled it and is wondering why it stinks like that. Just another level added to the problem that needs an alibi set up for it - so you tell your friends a story that to you at least sounds plausible and you put it off another couple days until you can't stand it anymore and you're desparate enough to dump it. The problem now is the car...
casey most likely made sure of that oh god typing this makes me cry and breaks my heart 
