LrdApoc, thanks for chiming in - it's given a huge perspective boost on the situation.
My strongest suggestion would be that Cyree's player needs to spend more time interacting with LrdApoc and Mark (the other guy). SHE can be their go-between, between the DM and themselves. LrdApoc, you say you and Mark just don't have time to dig deeply into the Campaign current events (4 kids - no need to explain ANY FURTHER

) then why not have Cyree's player, at the beginning of each session, give you both a run-down (in or out of character) on not only what SHE wants to do, but what EACH one of your characters would find beneficial. Make it a round-robin, where the whole group tackles one goal one week (or for a short arc), and then tackle a goal next that Mark's PC would want to, and Cyree gives full attention to helping him achieve that goal, WITHOUT dominating the scenes.
She still gets the immersion she wants (she's the lifeline between your group and the world), but the other two players get to shine a bit, from arc to arc. This solves having to send out e-mails between games, spending a lot of time character-developing outside of Game Day, etc. You all need to confine all out of game planning to game day only, and work with what that gives. Cyree's player can correspond with Crothian about her PC till they're exhausted, and she can compile ALL of the group goals (not just hers) and get ready for the debriefing each week.
The important thing is for her to find out what Mark's PC would want, and try to draw up all those goals so that in-game he can make a decision and the group sticks to it. Nobody should be telling Cyree's player to limit her involvement, but it's not unreasonable to ask her to help out two friends when she's got more time to devote than they can.