Can I get some comment & critique on the beginnings of a story I've got going? (x-posted from my tumblr)

A shapeshifting carnivorous plant alien comes to earth. The first half of the story is framed as a horror story with the alien disguising itself as a woman and revealing itself to eat humans, standard monster movie fare. The change in the story happens when we meet our real protagonist, a college girl with a secret, she’s also a shapeshifting creature, but one that’s quite a bit more benign, she started out as a government project in splicing human dna with other species. and now sometimes involuntarily shifts into the form of an insectoid lizard creature, but on the plus side can also disguise herself as anyone she wants.

So for a while we follow our protagonist as she lives her daily life, just trying to be an average girl in spite of the inconveniences of her powers. Although also sometimes taking advantage of her abilities to get ahead, intimidating homophobic frat boys by shifting to a dean, scaring off some nazis by shifting to the largest and most imposing biker she can find. You know, just being a low-key do-gooder as much as she can with shapeshifting powers. The times where her beast form comes out she’s managed to keep under control with the help of her biochemist girlfriend who’s come up with a formula which provided she takes it, allows her to treat it as just another form to shift into.

Meanwhile, we’re finding the alien plant is starting to develop a curiosity towards humanity, and by now has found a form that it prefers to stay in. That of a particular woman it saw in a fashion catalogue. The alien begins to settle into an identity as this form and while the predatory instincts are still there, remorse is beginning to form as well, and she resolves to only feed on those with predatory tendencies themselves. It’s at this point that our protagonist comes across her in the midst of chowing down on a well known campus rapist, and, much to plant girl’s surprise upon returning to human form, isn’t horrified.

I haven’t got more than this figured out, but the crux of the story will centre on our protagonist and plant alien girl on the run from authorities who mean harm to both of them. They also eventually also end up dating, including the previously mentioned biochemist gf.

Edit: A friend of mine suggested I either do prose or comic form as the medium, though as this'll be my first time seriously writing...well, anything, I'm wondering would it be better to stick to a completely text-based medium?