Children’s Fantasy chapter book with Green Cat. Read around 2015.

[Francis]

Looking for a book read around 2015 about a girl who goes to a magical world, don’t remember many plot details but there was a green cat. The cat was white in the beginning but turned green with magic (maybe by the girl’s magical powers?). I think its name was Lucky or something along those lines.
I’m pretty sure it didn’t mention the cat in the title. It was a paperback and I got it from my school library in 4th grade.

[SBC]

This is probably not your book but I'll suggest it as it has a green cat and they are fairly rare! Green Is for Galanx

[Genesistrine]

Fritz Leiber's The Green Millennium also has a green cat, but is very definitely not what you're looking for!

[Kris]

Francis, can we eliminate The Missing Magic by Kallie George?

Google search of Goodreads:
site:goodreads.com "middle grade" "fantasy" "green cat"