Hello!
Cavies are generally very scared at first. Especially younger ones. They take a while to warm up to everything. Eating is very important, but she is likely eating when you're not in the room. Usually piggies know that they should be eating and do it! However, if you do think she is not eating, there are a few things you can do.
First off, feed her from your hand as often as you can! While she's warming up to her new home, she's also warming up to you, and eating from your hand can help her get familiar with your scent.
Try to show her how to eat and drink! For water, what I did when I first got my piggy was I would tap on the straw of the bottle and that would usually get my her attention and she would be interested in what was going on. You might notice they will often follow your hand, so you can use this to your advantage! You can put your hand at your piggy's mouth and lead her to the bottle. Then she gets some water and realizes it's right there and she can drink whenever she wants!
With food, do similar things. Maybe shake the food bowl around, lead her to it with your hand, and stuff like that.
The last thing I would recommend is to get her a friend. I know that they can be very expensive and hard to find, and you may not be in a place where you can get her a friend, but if you can, please do!
Guineas are very very very social animals and do much better on my own. I myself am a new guinea pig owner and I got my first cavy on her own, and now that I have two, they are much happier together! Getting your piggy bonded with a friend is also hard after you've already had your first one for a bit, but in the long one, it will be worth it!
I hope this helped