As for your question, unless you know one of the parents was indeed a British Shorthair, it is a domestic short hair. However, look a likes can happen and your little one does resemble a BS in the photo provided. I see you are in the UK so perhaps it's more likely there is a mix than if you lived elsewhere.
small kittens do often have this Teddy Bear looks. So we really dont know what she will be. Probably not modern siamese, but there are quite a some looks she may gets...
But yes, at this moment she looks quite alike the British shorthair, kitten...