I'm not sure what the time manipulation strategy is called, but I refer to it as The Fried Green Tomatoes technique. I like this strategy in this play. It makes it more interesting than if it were a straight through narrative, I think.
You introduce a lot of characters in scene 2 that seem unnecessary. This is kind of confusing when I first read the play and was trying to figure out who was who and where they fit into everything. I can see the purpose of Sarah in how she pops up later on, but not much with the other characters. Why do we need to see Sam and Christina?
You don't differentiate between the scene with Julie and Carlie and the scene in the present with Julie and Amerie. There is a blackout in between, so there should be a new scene. When you switch back and forth between time, it helps to clarify things for the reader with a definite scene change.
I liked the flow of the dialogue and the structure of the scenes except for Julie's monologue at the top of scene 4. Lots of what she says seems too blatant, like she's speaking some subtext aloud. Maybe there are ways you can show these things without her having to say them outright.
What's with Amerie and her guy? You introduce some issues and they are never really explained or anything.
I wasn't sure at the end of act 1 whether or not Carlie died, was this intentional?
Is the ethereal voice that tries to get Julie not to take the pills Carlie?
I liked the resolve Julie has at the end. The fact that she made it through.