Is she eating hay? Is she potentially eating and drinking overnight or when you are not otherwise able to see her? Skittish new pigs often creep out at night to eat and drink even though they are not nocturnal by nature. Is she peeing and pooping (are you finding damp patches and poop in the cage?) Have you weighed her? I would start a daily weight to see how her weight is trending. If she's losing and not peeing or pooping, this is urgent and she needs a vet assessment ASAP.
Assuming she is peeing/pooping and not dropping weight, If she's new, young, and on her own, a lot of these foods may be new for her and it may take her time to figure out that they are, in fact, food. A lot of pigs from pet stores have never seen vegetables before and are not sure if they are meant to be eaten. This may be true if the pellets are different from what she has encountered before too. Pigs are social and will learn by watching what other pigs eat... they can be very skittish/cautious on their own. Keep on offering foods and in time she will be more likely to accept them.
As others have said as well, pigs are social and feel much safer and happier in a pair or group. If it's possible to have a pair, you will likely see a big increase in confidence and happiness in a young, nervous pig.
