A one to two year old boa should be on a 10-14 day feed schedule, imo. Even as babies they should be on a 7-10 day. Slow growing your boa is the best for it. They have a slower metabolism. They also should be fed a prey item that does not leave a noticeable lump. The rapid growth could be from feeding weekly. I would definitely space out to at least 10 days. Also, boas need much more room than a ball. I would not keep her in a tub for very long.