[nikasaur]

According to This! there's a pretty good explanation from Stemmle:

SWP: There are a lot of controversial talks between the fans regarding the story of ToMI. Can you clear it up a bit for us? For instance, is it implied that Elaine knows about everything from the start? How much DOES she know and what was her plan, if she had one?

MS: Elaine has a history of being one step ahead of Guybrush, LeChuck, and everyone else in the world of Monkey Island. That’s because, well, most of the cast isn’t all that bright.

Our take is that Elaine has long suspected that the Voodoo Lady has been putting Guybrush and LeChuck through a never-ending cycle of conflict for mysterious purposes. This annoys the heck out of Elaine, who is ultra-protective of her hubby and chafes at the notion of being manipulated by forces beyond her control. But Guybrush trusted the Voodoo Lady too much for Elaine to simply say “Hey, I think this nice lady that has helped you on umpteen previous occasions is using you like a puppet.” Besides, she didn’t want to get on the Voodoo Lady’s radar.

When LeChuck suddenly became human at the start of the first episode, Elaine intuitively realized that LeChuck was also playing some sort of long game against the Voodoo Lady, so she went along with it, keeping an eye on LeChuck all the while, and nudging Guybrush in ways both small (”trust me”) and large (”take the ring”).

Of course, she didn’t plan on being overwhelmed by the Pox. Or LeChuck actually managing to kill Guybrush. That’s why she’s so forlorn at the start of the final episode; she’s played things too close to the vest, and now her snugglebunny is dead.