Sally in particular is one of Blaze and Anubis' more Unique Size shifters they have ever had , Normally with Them and the other Growth favoring shifters their weight naturally fluctuates depending on their size as you would expect, but with her being a hybrid for some reason if she grows to say 300ft tall and to weigh 4000 tons, and shrinks back down to her 4'5" normal size she will still weigh that much until her body burns that density off, making her both hungry and super energetic in the meantime. Think like someone being hyped on caffeine only without the negative effects after, Her Current Max size is 8 miles tall, just over the average city size and she wants to grow taller still, even pass her mother's max height. Nicole's meanwhile is only 2 miles cause she doesn't like growing as much, Sally's Minimum size is 1 foot and Nicole's is now an inch thanks to Ember's training and she wants to go lower. Sally was told by her Mom and Dad she cant grow unless she is in a field or is off planet, cause otherwise she will cause tremendous damage to Wyndon otherwise. The roofs of the buildings in the town are designed to withstand the weight of Someone Nova's size since it would be spread out, but if she sat down at her normal size after shrinking back too fast she would break right through like a cannonball threw a piece of wood. However the way she can bypass this is by shrinking over the span of an hour, then she doesn't get affected by ether the weight rush as she calls it, nor will break the concrete with every step