Interesting. Haven't watched the movie but your description matches the synopsis and clips I have seen.
The novel is different, though it hits some of the same notes. Here's the gist of it, and be warned these are SPOILERS:
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SPOILERS
The main character is indeed an alien. She's a non-humanoid alien, hinted at to be a quadruped somewhat similar to a dog/wolf in her home planet. It turns out that humans are a delicacy to her race, harvested for their flesh. This is a low-scale operation (in order not to alert the humans), and for this they need a lure: she undergoes irreversible surgery to turn her into something that looks like a human girl with big breasts (on close inspection, there are some signs she's a flawed imitation, but most victims don't notice until too late). She finds her human form bizarre and painful, and cannot connect either with other workers at the human meatpacking plant (they remain alien-shaped) or with humans (until very late in the novel she considers humans as barely more than cattle, incapable of real feelings). She is an outcast in her own society, very low-class -- she cannot, for example, "pay" for the human delicacy she helps harvest; it's not for the lower classes -- and this job was an alternative to dying young in some kind of high-risk mining job, reserved for the lower classes of her race. She cannot ever recover her alien form and cannot connect with anyone; she finds the planet Earth beautiful, but not the humans that inhabit it. In the end, her situation is hopeless and she dies, which is a sort of release.