Is it normal for 7 month old?

Every baby is different. My daughter is 7 months and weighs 15 lbs. Everything that she picks up goes in her mouth. She started solids at 4 months, and eats them 3 times a day. She was a preemie and I was told she'd be behind developmentally, but she is right on target, if not ahead. She sits independently, but she refuses to crawl or creep. She still eats a lot of milk, every 3 hours, along with the solids. On the other hand, my sister's baby didn't eat solids until she was almost 9 months old. She was big for her age, and didn't sit up until 8 months, or walk until a year and a half.