IIRC, RM indicated the one occasion in which ICA left in the middle of the night to return Caylee home (most likely on CA's insistence) but that many, many nights in February through April, she spent the night at RM's with Caylee sleeping in his bed. I'm thinking it may show that ICA had threatened to leave with Caylee and perhaps actually did during those months to punish CA for getting on her case about stealing and other things she was obviously putting them through at home. RM and others mentioned that ICA sometimes had a problem getting Caylee to go to bed. This was probably a big embarrassment to her, not to mention an inconvenience. It would seem bad enough to her that her friends had decided to stay home to be with her because she could not get her mom to babysit, but if ICA had to spend a lot of time wrangling her to go to sleep I can see where that might have been the start of the experimenting with drugs to get her to sleep quickly. Whether it was OTC stuff to begin with, or xanax that ICA lifted from CA (who wouldn't be taking xanax if you had a daughter that was stealing several hundreds of dollars each month from your bank account?), it would seem logical for this to be the beginning of using medication to quiet Caylee. RM insisted that Caylee slept on the other side of ICA in bed (and didn't seem concerned about her waking up in the middle of the night for any reason) and Amy remarked how Caylee had been able to sleep through parties on the sofa.
I don't see why ICA would need to put her in the trunk during those months when her friends were certainly willing to forego going out to stay home and keep ICA company (which according to Amy was at least a weekly occurrence and that CA would babysit otherwise). But when she left RM's after that last week she stayed there (June 9 - 14) she may have known perfectly well she wouldn't be able to do the same thing with Tony.
Maybe she was just improvising this time and gave her something in her car seat but it didn't knock her out fast enough. Maybe Caylee wouldn't cooperate and was crying. We can all see that ICA can really snap when she feels pushed into a corner and "frushtrated". Maybe she got furious it was taking too long, or afraid the crying would call attention to her and grabbed the duct tape while Caylee was still in her carseat, bound her face, then put her in the trunk. Obviously she didn't know or care what would happen next; she was only thinking of not being late for her Blockbuster date. I'm wondering when or if it even occurred to her to check the next day, seeing as she and Tony spent the day in bed. I only say this because, as evil as ICA can be, it never seems very well thought out in advance, but stuff made up on the spot to cover for her lack of impulse control. She doesn't seem very good at any kind of follow-up and many have remarked she pretty much lives in the moment.
I always thought her insistence on the kidnapping in those jailhouse tapes, even after an accidental swimming pool death was mentioned as an out, was because she knew perfectly well that either a tox screen or the way the duct tape was applied would blow that theory right out of the water if she ever led them to Caylee's little body.