[Formendacil]

While, obviously, there is no evidence beyond the text just cited, it is truly delightful to speculate. Three possible series of events strike me:

1.) It was deliberate--if not malicious (we are, after all, talking not only about Hobbits but about Pippin's older sister). Pearl gives Lalia an irritated push and down she goes. The family punishes her to be seen doing the right thing, but gives her the jewels afterwards when Pearl makes a stink about how any of them might have been mad at her.

2.) It was an accident. Pearl was simply careless and the family (as before) punishes her for causing the accident and then rewards her to show they aren't *really* sorry about losing Lalia.

3.) Pearl wasn't involved. Someone else of greater stature--perhaps Ferumbras, perhaps his heir-apparent Paladin, perhaps Paladin's wife--is with Lalia the day she dies and is responsible for her death. To protect this very prominent figure, Pearl is alleged to have been with Lalia the day she died since Pearl was a regular attendant to the head of the family. Pearl is excluded from Ferumbras' accession to encourage the rumours, but is rewarded with the jewelry for helping defend the family honour.

I'm sure other theories--more or less variants on the above--could be devised. Personally, I favour 3, but probably because it's the most salacious. It strikes me this would make for excellent fanfiction: Agatha Christie locked-room meets Tolkien.