I've often wondered if MC called RC because Haleigh wouldn't go to sleep, and he suggested that she get into his "medication" and give her a half a tablet, something like that. Didn't Haleigh have some respiratory issues already? Many medications for pain or anxiety can depress the respiratory system - and they can be VERY dangerous for someone whose system is already compromised.
If MC either went to sleep (which now seems doubtful) or left, it's possible that Haleigh was in bad shape by the time she returned. Could be that she called someone to help her, and that might well account for the "bouncing on the couch", as you pointed out.
If that scenario is correct, RC wouldn't have had to be home in order to be responsible for what happened to Haleigh - and if the medication given to Haleigh was obtained illegally, then he'd be in some mighty deep trouble.
My head is spinning with all the newest information, and all the possibilities. Could be that RC and MC are equally culpable, and are covering for each other. Who knows anymore?