My scenario has always been similar to this....
Parents up, go to work...
Holly has been up studying, getting ready for school.
Clint is sleeping or at least not up and out of bed.
Holly leaves the house. She goes out the back door to her car in the car port. I am assuming this back door leads into the back of the garage. She is startled by someone. There is some discussion or scuffle. He may have struck holly. This is when the dog starts barking and Clint wakes up. He has heard the voices outside.
Based on what Clint said we know that Holly and the suspect were in the garage, aparently after he heard voices outside. Perhaps Holly tried to go back into the house? Perhaps the suspect, thinking Holly was alone, started to take her back inside?
Possibly after being struck, Holly is kneeling in the garage, and the suspect is with her. This is when Clint sees them, aparently in silhouette. So he does not see much detail. Possibly the suspect had become aware of Clint and was trying to hide by kneeling (with Holly).
After Clint leaves that part of the house to call his mom (all this is murky in Clint's description) the suspect and Holly leave the garage and walk up the back of the hosue through the yard. Clint sees them out a window...
At some point after the suspect is away from the property with Holly, she screams. Maybe he is trying to tie her, gag her, put her into a vehicle? She is closer to a neighbor and the neighbor, who is outside at the time, hears the screams and call 911.
I do not think the screams happened first. If the screaming had been first, then the phone calls would have been earlier rather than later, based on what little we know about the calls.
Addendum:
I also dont think she would instantly start screaming, then very calmly and quietly just walk along next to this guy going into the woods. Doesnt make sense that way. I can see her being calm and cooperative at first beucas maybe she was hit or threatened, but then paniced and screamed later on.