I would think that this would be a conversation you need to have with Grayson's nutritionist. My guess is that with a feeding tube and continuous feeds (even if just at night), they'll want to keep her on some type of formula.
My dd was already really struggling to gain weight at a year, but did not have a feeding tube at the time. We switched her from breast milk directly to pediasure right around when she turned 1. Now she drinks one pediasure orally and takes 2 Boost Kids Essential 1.5 through a continuous night feed.
A lot of the pediasure type drinks are for kids 1+, so I'm guessing her birthday is opening a lot of options for you now to get weight on her and get her to grow.