Can anyone tell me what breed she may be?

I have a 3ish year old cat named Monster. She has a very unusual coat pattern. She was dropped off at the shelter under a year old and pregnant, all of her kittens has identical markings to her. I've had her for 2.5 years and my pet insurance company want to know her breed. I guess I never really thought about it that much.

Could you possibly post a picture?

Also, cats aren't really purebred unless they come with pedigree papers.

So your cat is most likely a domestic short, medium, or long haired cat.

Cats can resemble specific breeds, but without pedigree papers, they cannot be officially classified as any specific breed.

If you post a picture of your cat, someone may be able to tell you which breed your cat most resembles though.

She's a gorgeous domestic short hair.

She has a tabby pattern and lotsa of white.   This combination of some coverage on head, and tail, the rest white, is called for a Van Pattern, after the Turkish Van whom made the pattern renown.  Now, turkish van are rare, but the pattern isnt unique.

As you yourself witness, its not unusual a barn cat out of nowhere has a whole litter with identical pattern...  Usually its a strong indicium for being purebred, but this is one of the exceptions.  A strong pattern.

So, she is a domestic for the insurance purposes.  If you must describe her, so tabby and white in the Van pattern.