This is really, really easy unless <PERSON> doesn't know very much about how to use her magic or about the natural sciences. If you want to make it a challenge, you'll need to decide what she doesn't know (once you learn more yourself than she would know).
Firstly, as has already been pointed out, <PERSON> doesn't need food to survive, just water, and maybe not even that (depending on the weather). There are plenty of cases of people lasting far longer. As long as she didn't get lost (she might), and didn't waste too much time searching for food she couldn't find, she'd be okay.
But there are much better opportunities than that. She can use her energy to replenish her cellular ATP stores. Turns out that human metabolism is only about 40% efficient. If she gets 50% more from magic, she can cut her food consumption in half just by regenerating her own ATP, or power herself for more than one extra day from the stored energy alone.
But then, why is she walking? Walking isn't very efficient. Cyclists going 20 mph (over 5x walking pace) use only about 100W to overcome air resistance. If she can perform any sort of levitation (and how could she not, being able to move molecules so easily?), her 4 MJ would let her travel for some 40,000 seconds at 20 mph, giving her a range of some 220 miles. 790
I suppose she can't use this, though, or she'd have lost her pursuers in a few minutes instead of two days.
So suppose she wants to hunt. Animals don't do very well without oxygen; all she needs to do is pull the oxygen away from an animal and wait for it to collapse. Or she could depressurize the sky around a flying bird, and go pick it up after it crashed to the ground.
But you don't even need to go after animals. Trees have sugar in them; pull it out and eat it. You can get water from trees, or from the soil. Even bacteria use sugars and fats to store energy; if you can manipulate molecules you can summon hunks of fat, sugar, and water right out of the bacteria in the soil. Or, since forests have high humidity, just pull water out of the air.
So this isn't an issue, really, of what's magically possible with this kind of magic. It's an issue of what <PERSON>'s limited knowledge and experience allow her to do. And there, the best choices are ones that fit with other parts of her story. 227