She's 20 pounds, 6 years old. She has a weird throaty meow that I've never heard before. She sounds like a mafia gangster cat/ a crow. She looks like a chartreuse, but she has white under her neck and on her belly.
She looks like she might have a bit of British Blue in her. She has the same thick, dense coats like they do. Her face is not quite as round as a British Blue but she still has the same sort of look.
Brits are also typically rather round, which may explain both her weigh and part of her "excellence appetite"- look.
But still, you must look up with this excellent appetite... What are you giving her? Wet canned food is the usual tip for slow, safe decreasing of excessive pounds.