I just checked a classic flavor (cod, sole & shrimp) and indeed, it's grain-free. I'm surprised, but there are those nasty by-products. My cats were less interested in the FF today (tuna & cheddar), so maybe there's hope.
Is that weight gain normal for a kitten? Maybe she's outgrowing the kitten stage and doesn't need as much food, but is eating it anyway, then throwing it up?
One of my cats throws up fairly frequently - it's either because she ate too fast or because she's got a hairball. If it's a hairball, she often makes those wheezing or hacking noises first. Is that what Pia's doing?