Runt of the litter?

We have 2 shelties. A 1 year old Tri (Buddie) that is 27 pounds and a 7 month old sable (Kittie) that is only 8 pounds. I don't think she will get even close to 10 pounds. When I google about small shelties I see people writing "my sheltie was only 12 pounds" and I laugh. Our first sheltie topped out at about 30 pounds. Any thing we should look out for with such a small sheltie? FYI both came from reputable breeders, Kittie was half the size of her litter mates but we thought she would get to closer to 14 pounds. Vet says she is healthy.