Couple of questions regardin my Maine Coon

[sarriux]

Hi everybody,

I bought a Maine Coon female 3 weeks ago and I have couple of questions. When I brought her home 3 weeks ago, she was 5 months old and weighted 2.7 kg (6 pounds), now she is almost 6 months old and her weight increased only to 3 kg (6.7 pounds). Is she is not too light for her age? Is everything is normal with her size and weight at this age, as the breeder said she will be around 6-8 kg (13.5 - 18 pounds) at full grown.
Another thing, I have the pedigree certificate and as I can see, her mothers father and fathers father is the same cat and inbreeding perscentage for 4 levels is 10.5%. Is it ok with this or is it too high?
Thank for your answers.