Being separated from the Newbies, Willow doesn't have to race the others to finish her food first. I wondered if she was eating less hay/pellets because she lacked the competition that most pigs seem to thrive on. I'm concerned: Willow has been dwindling very slowly over the last several months. It's probably a mixture of old age (she'll be 8 in May!), arthritis and possibly another bladder stone. So I want to encourage her to eat as much as possible to keep her weight up.
Hay is the one thing I can present with a challenger. I stuff a handful in the grids between their cage 2-3 times a day. In classic guinea pig style, Willow will walk away from her own stash of hay to match up against Bertie or Pinni for the best pieces in the bunch.
If Willow is lucky, she manages to pull the last loose pieces onto her side of the cage for the win. It's a rare event. Usually I find the remains on the Newbie's side.
Regardless, it motivates her to stop living in her own little world and interact with the other pigs. I think she eats a little more hay with the competition. It also drives Pinniped nuts, which can be entertaining. Pinni still wants to guard or eat all of Willow's food. I've even witnessed Pinni trying to stuff her nose through the grids to eat Willow's pellets.
So the grid divider layout seems to be working well. It's a much better setup than when she was in the old cage. I've seen them all socialize a bit between the grids. And it gives Willow the opportunity to snatch the best pieces of hay from another pig. Go for it, Willow!