Have a look at the photos available online from that party - there is the one of her with the blue streamers and the cake, and the outside is visible on screen right - its around dusk. The sunset that day was at about 6:21pm that evening (I googled).
So if they'd had cake soon after, what time do you imagine the party ended at? Couldn't have gone much past about that point if they had cake around dusk - maybe ending between like lastest? 8/8:30pm if not a bit before based on what time the cake was likely done and nothing more - so MOO - but she probably didn't get home much later than what 9? If she left after the party when guests were gone and maybe some light tidy up or relaxing with host was over? Just guess this is NOT facts. So we're supposed to believe this 13 year old girl went home and just went directly to bed? Couldn't have been a late bedtime then.... and I don't buy it.
Were ALL her friends at the party? There was NO ONE she wanted to talk with and show her gifts to? Not one kid that couldn't make it due to some other commitment or illness (if any were even invited??). I think the idea that she went straight to bed is a lie, or a cover up for something. I'm not convinced she even made it home *safely* that night.