Oh god, he's getting her to like food....
Her body is probably highly efficient at breaking down the air molecules around her and turning it into energy, so with the sudden intake of whole foods, her body is probably gaining MASSIVE amounts of excess energy. Because of the exceeding amounts of energy her body is taking in, it's probably causing her brain to release huge amounts of dopamine as well (dopamine is the "Pleasure" chemical), so she might LITERALLY be getting addicted to food, wanting more and more of it to get more and more dopamine. By the time she's gotten used to eating food, her body would have adapted to the increase of energy, meaning that her body is most likely much less efficient at absorbing energy, both from the air, and from eating, meaning that once she starts eating food at regular intervals, she will no longer be able to sustain herself with just air, as it doesn't give her the necessary amounts of energy that she need to survive. SHE WON'T BE ABLE TO SURVIVE AT HER HOME PLANET ANYMORE. Also, once she gets used to having food regularly, the amount of dopamine that her body would create would be substantially less than the amount she had when she first started, so she'll start having WITHDRAWAL SYMPTOMS. FOOD IS LITERALLY A DRUG FOR HER. SHE NEEDS TO STOP.
tl;dr - Food is a drug for her species and if she starts eating food regularly, could possibly cause her to no longer be able to survive on her home planet without some form of long-term rehabilitation program. STOP HER FROM EATING.