Just to add to some very very good answers, here are my 2 pence.
Talk with them
RPGs are a group activity, an activity in which a group of friends come and talk with each other about fictional characters. The main thing here is the "talking" part and from here I believe that your solution should come. Talk with them after the session; understand why they can't write those long-long pages of fluffy material. Maybe you can help them, maybe you can solve the problem or maybe you can't do a thing, but you'll be much more understandable of their situation, and due to the knowledge it will be much easier to know what to do next.
Focus for one session on this particular player
A bit risky option, but one that I've used in the past a few times revolves around focusing an entire session on this player. The idea here is to draw the players' jealousy and from that persuade them to write those extra pages. "Wanna the same focus as Lisa? Do this pesky extra work and you'll get the same focus also."
Ask your CP to sit with them
Maybe the creative player can help them to overcome whatever is holding them down. Maybe if she'll sit with them they'll be able to write those extra pages too. When you've got those pages, you'll have much easier time coming with plot hooks that connect them also.
If they have a background- tie them in
If your other players wrote backgrounds at the time, use it: Tie them in. Find those places where there are holes in their background, or where they kinda connect with the background of other players (preferably the CP) and roll from there. It will give you the excuse to add those players to much more scenes, thus changing focus from the one CP to the entire group.
Channel the CPs creativity to other places
Surely there are places in your world that haven't been defined yet, why not using the CP in order to define them? She has the creativity, and the time, and it is a really nice way to channel her creativity without giving her character more reasons for extra screen time. Use that to your advantage.
Sometimes, and for the short term only, you should give them something in return. To some players who haven't tried yet character focused scenes, those scenes don't seem yet as a real reward. Until then, maybe another kind of reward is preferable. Maybe this is all they need to start those engines.
And an end
So these are my 2 pence on the topic, all hope that it will help you.