How old is the bunny? Generally, you’ll want to feed babies alfalfa hay. I’ve seen that they can have it until they are 1 year, but I started phasing my bunny off alfalfa hay to timothy hay at 6 months. Alfalfa is more nutrient rich than other hay, so it’s great for growing bunnies to have. It is too rich for adults, and will just make them gain excessive weight, this is why it is only recommended as a staple for young bunnies.
Sometimes baby bunnies take a while to settle in. When I brought my 8 week lop home he didn’t eat much for the first two days, and he didn’t really get a “normal” appetite (where he was eating all his hay throughout the day) until about a week. Maybe she needs a little more time. For hay, you can just switch it. Pellets and veggies need to be introduced slowly but hay is fine to switch instantly, from my understanding.
As a new bunny owner (I’m assuming it’s your first time?) it’s very important that you familiarize yourself with….her poop. I know, it sounds strange. In rabbits, their poop can tell you many things, depending on size, color, moisture, etc. There is a great poop guide on here, I believe it is in the diet & care section. Their poops should be a firm ball, but easily squish between your fingers, and inside it should just look like, well basically like you threw some hay in a food processor and ground it to tiny pieces. Yes, you will need to squish the poop and check out the inside too! 