Welcome! Does she have a friend? Guinea pigs learn what is safe to eat by watching others, my 2 newest babies didnt touch bell peppers for their entire 2 week quarantine but were happily munching away the first meal they got with my herd
It can also take quite a while to figure out what is food, about 18 months ago I started offering butternut squash and it took a few weeks of offering it before they actually started to eat all of it, rather than just nibbling.
Herbs are a great way to introduce fresh foods to them as they smell quite strongly, I find chopping a herb they like to eat over a new food can encourage them to have a try.