My chihuahua is 4 months old and 41/2 lbs? Isn't that huge for a chihuahua?

On chihuahua growth charts for 16 weeks, the max weight it has is 59 oz. (3lbs 11 oz). I think my puppy is going to be abnormally big for a chihuahua. I found a site that said double weight at 4 months and add up to 10 lbs but that would be 9 lbs at the least! Thats huge for a chihuahua. She was the runt and her parents were about 6 and 7 lbs each. Any reason why she's so big? Breeding standard is 3-6lbs i think.