That her tummy is growling is indicative of gas. It’s more serious than you might think, gas can cause the gut to slow down, leading to full GI stasis, and a build-up of gas can actually lead to a deadly and extremely painful condition called bloat. The gas needs to come out asap. You should sit the bunny in your knee and give her a gentle tummy rub. Here’s an instructive video on how to massage a bunny’s tummy, but if your bunny isn’t as compliant as the bun in the video, you will have to adapt the method to your situation: https://www.youtube.com/watch?v=JnuxGLa2reg
You can give her baby gas drops (simethicone) so the gas breaks up into smaller bubbles that are easier to pass. It’s available in most normal food stores and/or pharmacies, depending on where in the world you are located. The amount you should give is about 0,5 – 1 ml of the drops.
It is very advisable to take a new bunny to a vet for a check-up. You can call your vet and describe her symptoms. It is great that she’s eating hay and greens, esp hay. Has she pooped? If a bunny doesn’t poop in 12-24 hs, it’s a veterinary emergency and you need to take her in.