I'm trying to think of a good reason why Lavinia doesn't go with the party to Tanaroa. She's got more diplomatic skill than anyone in the party, and perhaps being a female will have an advantage in a matriarchal society. I guess you could say she's running for office, but given the gravity, that seems like a frivolous reason not to go. Also, why wouldn't the Jade Ravens go?
Do the players want her to go and do the job for them? If they aren't asking her to go, then you don't really need anything more than she is busy running for office in Farshore and wants to keep an eye on Meravachi.
If they are insisting that she should do it, then I guess you should ask them how much they want Lavinia to be a member of the party and if they want to have someone take the Leadership feat so they could make Lavinia a cohort.
Give the Jade Ravens another assignment...like the troglodyte settlement or helping another Olman village.