Shapechanging: Ariel has two types of shapechanging. Human shapeshifting and gross shapeshifting.
As she is intimately familiar with the human body, Ariel is a master of human shapeshifting, able to stretch and squeeze her biomass into just about any human shape. She can easily replicate specific people given time the study them, though for the most part she enjoys creating and discarding faces at a whim. She generally likes to be what she considers to be beautiful and at any given time she'll usually have two or three faces she likes falling back on out of habit. When she changes into a human shape, for all purposes this shape is considered her 'default' form. If she were somehow rendered unconscious she would not resume her original form, but would resume her last human shape. When she is emulating human form, she is capable of emulating human bodily functions, such as a heartbeat or functioning lungs, at will. She can bleed if she wishes, though the blood is made of the same stuff as the rest of her. Similarly, when she adopts human shapes, she is capable of using her shapeshifting to clothe these shapes as well. The clothes look like ordinary clothing, but are a part of her biomass. She has a limited ability to split off parts of her mass and either reclaim them or let them go. Which is to say that if she is wearing a form that has a hat and ends up having to drop the hat and does not absorb it back into herself, it will eventually disintegrate.
The second aspect of her shapechanging is gross shapechanging. She is able to alter her body freely to the limits of her biomass. She can stretch her arms, grow new limbs, alter the density of her cells from flesh to bone to the concrete of the golem, grow natural weapons and armor or flatten herself to allow for brief gliding. Her gross shapeshifting might allow her to take on animal characteristics, especially if she sat and attempted to study or emulate an animal, but ultimately it would be very obviously not real and very wrong, because she simply lacks the fine control when going outside of a human form. Her shapeshifting is very obvious and can be quite disturbing when she abandons human shape, becoming a biological abomination, her body both flesh and stone. At its most extreme, should she find herself in a fight, she can pile on the changes becoming a ten foot tall monster, bristling with claws and fangs and spikes, layered with armor plating, strong and fast and wholly inhuman. She can combine her human and gross shapechanging abilities, but when she does the results are frequently horrifying, like something out of Cronenberg or a Hitoshi Iwaaki comic.
Physical: In her human shapes Ariel is significantly stronger and faster than a normal human of the same height and body type. However, when she begins to exercise her biomass she can increase the density of her muscle, grow layers of armor, becoming superhumanly strong and durable. Due to the homogenous nature of her form she is almost entirely immune to physical damage. She has no internal organs to damage via piercing or impact, though a strong enough impact can certainly jar her. She is also innately resistant, especially when armored up, to other energy attacks, but not to the same degree as she is against physical attack.
Rapid Healing: She heals rapidly in the course of combat and even moreso once she is given an opportunity to rest. Her biomass is capable of eventually recovering from truly greivous amounts of damage. Due to the nature of her makeup, wounds, even maiming wounds, quickly repair themselves. If significant damage is done it takes the form of missing biomass and is not necessarily obvious from looking at her. Similarly since her body is homogenous and even in her human form she has no organs, shocks to the head are meaningless, her consciousness evenly distributed throughout each cell.
Adaption: Due to her physiology, Ariel does not need to breathe, sleep, drink or eat* and is immune to most drugs, toxins and diseases. Additionally, her shapeshifting allows her to adapt to most environments, whether the depths of the ocean, the hard vacuum of space, a frosty polar clime, the radioactive fallout from a nuclear meltdown or the burning and corrosive caldera of a volcano. Note that none of this means she can adapt to direct energy assaults. This is about surviving environmental rigors. She is capable of walking through the choking sulfrous mists to the edge of the volcano, but she would not enjoy leaping into the lava. The saw way, she cannot adapt to lasers being shot at her any more than her extant resistances allow.
Weakness to Sonic: Ariel doesn't like loud noises anyway, and the louder it gets the more she doesn't like it. You're never going to find her at a concert because there is a point where the noise starts to hurt. Standing near speakers at a concert, sitting next to a stock car revving its engine or a sustained jackhammer would rapidly begin to wear on her physically and mentally. A directed sonic assault is not only devastatingly painful to her, but will cause her bioform to rapidly break down, she will lose control over her ability to keep a shape, becoming a writhing mass of flesh and stone and pulp, incapable of acting to attack or defend herself. Even a short sustained sonic assault will negatively affect her ability to shapeshift for days. If the attack goes on long enough it can kill her.
Powered by Meat: This is where that * back in Adaption comes in. In general Ariel does not need to eat, however extended use of her gross shapeshifting, especially to generate the extra biomass necessary to assaume her towering battle shape, or recovery from damage that causes biomass loss, requires that she replace her lost biomass with proteins. Raw proteins. The fresher the better. Which is to say that after a rigorous fight, she needs to eat raw meat, lots of it. The worse the fight, the more she needs to eat. Delaying this hurts both physically and mentally. Delaying it too long can drive her mad with hunger. Given her increasingly alien nature and decreasing regard for human mores, the potential implications are somewhat dark. Should she be aware that a fight is coming she can 'pre-game' and gorge herself so reduce her hunger pangs afterward. Thanks to her shapeshifting even if she gobbles down a hundred pounds of raw beef, she can maintain whatever shape she prefers. It will just be very dense.
Increasingly Inhuman: The further Ariel gets from the person she once was the further she gets from being human. She has the golem's memories, but being clay and stone and unintelligent it doesn't have an awareness of itself the way a human would, so that just leaves her with a vague sense of the ancient and occasional ghost recollections of far off places and times. Additionally, she has the sentience from the cancer, a ravenous viral thing that wants everything to be it. Between these two very inhuman points of view it's very hard for what was once a simple teenager to hold on to who it was, especially since the nature of her abilities means she no longer has a fixed physical identity. She's fighting to be human, but sometimes it seems like it would be easy to not. Her art and appreciation of human beauty are two ways she tries to cope.
Absentee Parents: Ariel's mother and father are horrified by what they've done and what their child has become. When they called Coral Springs to come and collect her they turned around and told people the cancer had returned and she died. So far as the school is concerned, she is their ward for two more years.