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Without seeing the DNA markers it's impossible to say, but she looks every bit a purebred Maine Coon kitten - good muzzle conformation and good ear set - though very few breeders would permit a kitten so young to leave the cattery. She's a beautiful girl.
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Very young so if she is purebred the cattery probably isn't registered themselves, a registered cattery always keeps their kittens until at least 9 weeks, usually until 12.
She looks promising, but only time will tell and her size will be a real indicator.
Let us have a look at her a year from now and we'll be able to tell better. She does look like she has tufts at the ends of her ears and her face looks much like a Maine Coon should but she's really too young to tell much about her. Have you seen the parents?
Looks like a Maine Coon, but it will be easier to tell when she's older. Do you know what her parents, or at least her mother was? She's so adorable!!!