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Adrenaline
The Fight or Flight response is a nasty one for Dana. She's put a lot of effort into learning to keep calm in stressful situations, but there's only so much you can do with her lack of experience. It's like this: the more scared or angry she gets, the harder time she has maintaining her form. If it were just that, it wouldn't be too bad. But her true form isn't the young woman you see walking around day-to-day. Her true form is like a roiling mass of flesh and limbs and tentacles and organs. Her true form is some unholy abomination from deep within some void. She might start a dog, but you hit her on a the nose with a newspaper and she starts looking more like some Lovecraftual quaduped made of pink flesh and sharp spikes pretty quickly. Put her in a blind rage or panic, and her true form comes out in full. Good luck avoiding dozens of tentacles and devouring maws, all superhumanly strong and resilient. Not to mention that she loses herself to primal instinct whenever it happens. She is terrified of this ever happening, and she won't ever use it deliberately except maybe (only maybe!) in the most dire of life-and-death situations. She fears people simply knowing her true form as much as she fears accidentally hurting someone when she isn't under control.
Dreamless
Whatever gives the human mind dreams isn't present in Dana's own head. Instead, she's connected to some primodrial void. This is what she sees whenever she sleeps, and it tends to leave her quite unrested no matter how long she tries to sleep. Any oneiromancers who might try to help her in the realm of sleep would find it simply impossible. This might be considered an advantage, but a relative lack of oneiromancers in her day-to-day life means it hurts her more than helps.
Fire
It's not really fair to call this a weakness. After all, even if she's burned she still heals in days what would take humans weeks or months. It's still a weakness relative to her, however. It's simple: cauterized or burned flesh is harder for her to regenerate, and it's much harder for her to move the injured area. A little bit of time with a flamethrower or a superheated weapon would be enough to make her useless very quickly. It's worth noting that she isn't any more flammable than normal human flesh; getting briefly singed won't cut it.
Hunger
Dana's new body is hungry. Given that it has no stomach and can simply keep consuming (probably) infinitely, that hunger isn't really sated with food. It can only really be dulled. Worse, it hungers for anything organic, not just people food. More than once she's found herself drooling at some dumpster despite eating lunch moments prior. Even more unsettling, it seems to prefer the dead. She nearly lost it once when she saw a human corpse and wanted nothing more than to swallow it whole. Mostly she tries to deny it happens, but sometimes she feels herself drawn to eat something she finds disgusting. She usually makes a sandwich instead.
Shapeshifting
The better Dana can visualize the form she wants, the better she can hold the form. If she's only ever seen a photo or video of the thing, it'll always look fake to anything more than the most passing or distant glance. She also won't be able to do much more than walk around before losing control of the form. Best results come from things she's observed in person. It's even better if the observation was recent, as this degrades along with her memory of the thing. This limits her mostly to shapeshifting to people she has met in person, or animals that live in the area (or a nearby zoo, though you usually can't get close enough to the animals to be effective). It's also noting that she has a really hard time fooling biometric security. She'd have to examine the part to copy very closely to memorize every detail without flaw. She doesn't have photographic memory, so she can't even maintain this for more than a few minutes after doing it before the flaws in her memory start expressing themselves in her form. Her DNA remains her own (and obviously inhuman at that) regardless of the shape she takes.
Uncanny Valley
Dana is creepy. Very creepy. It isn't even her fault, really. It's been so long since she was actually human that her memory of herself has started having imperfections. Inconsistencies. Look away and look back, blink, or even just look at her for too long? You'll feel something off about her. Wasn't her eye a lighter shade of brown a second ago? No, it couldn't be. Weren't her cheekbones higher? Weird, I must be imagining things. It's unsettling to just about everyone she encounters for anything more than brief pleasantries. It's more pronounced when she shapeshifts into something not herself. You'll see a dog and just somehow know something is off about it. That bird flying in the sky will make most normal people want to get a ceiling between them and it. It makes her power difficult to use for things like infiltration. She can, certainly, but people will be on their guard no matter what guise she takes within moments of observing her. It's usually subtle enough that it amounts to gaslighting rather than anything someone could prove (though see the adrenaline weakness for a greater extreme), but it marks her and makes her constantly uncomfortable in her own (or anyone else's) skin.
Vas Vacui
What is the importance of this book? Why does Dana keep it with her always? It's simple. The forbidden tomb Vas Vacui is the only thing that allows her to maintain control. If it moves more than a couple of feet away from her, then she loses her mind. Quite literally. She becomes a primordial creature of the void in body as well as mind, completely free of her mind and sanity until it is returned or she is destroyed. In a world with people like Superman, she'd be a relatively low-level thread in the grand scheme of things, but she really isn't looking forward to seeing how that would go for her. Not to mention she's terrified of people seeing her for what she really is.
