I would like to know what breed my cat is. I think she's mixed. I've always thought she was part Siberian and Maine coon. Supposedly, she's tabby but she looks very different from a lot of tabby cats.
Tabby is a coat marking, not a breed in itself. So while it's true that your beautiful cat is a tabby, that just refers to her pattern (indicated by that "M" on her forehead), there is definitely some clear breed influence in her. I think her face looks very much like a Maine Coon!
I agree she looks like a possible Maine coon mix (she looks a lot like my Maine coon), but without knowing her genetic background she would be classified as a domestic long or medium hair. As said tabby is a coat pattern not a breed, so she would be a brown tabby, there is more then one type of tabby pattern though. She is likely a mackerel tabby, but could be a classic tabby, or even a spotted tabby, without seeing a pic of her whole body I can't tell you for sure which.
Very much Maine Coon looks, face and mane... If she is biggish, the diagnose is practically clear. I presume you live in North America?
Of course, beside purebred MCO or mixes thereof, we do also have the natural population, from which the Maine Coons were purebred from. That is why we do HAVE so many MCO-look alikes in North America...
So these arent poor cousins from the country, they are representants from the Forefathers and Ancient Mothers.