How much do you feed your maine coons?

I have a maine coon girl, she's 9 months old and she was very skinny since she was little. I thought she would get some fat when she gets older but she stil hasn't, should I just wait even longer? I was looking at those charts on the internet and according to them she is definitely underweight like if you just pet her you can feel her bones (it's like she has no fat). When we were at the vet they didn't mention anything about her weight, she is normal weight for a house cat but she is much longer and taller (the vet doesn't know much about maine coons), I feel she should have at least few more pounds. She eats high quality kitten food, we free feed her dry food and she eats about 2-4 cans of wet food (100 grams each). And she gets vitam paste every day. I would like to hear some experiences and advice from other maine coon owners and how much do your cats eat and how big are they?