I am “new” to this but had bunnies growing up and they loved to nibble on grass. Hay should make up the majority of their diet and hay is just dried out grasses (different types but still grass). The main danger of eating fresh grass outdoors is if pesticides are sprayed but unsprayed grass is completely fine. Should be fine for a younger bunny as well but just watch for any tummy upset (as a precaution).

The short answer is yes, rabbits can eat grass.

The long answer is yes and no

Obviously if the grass has been sprayed with pesticides you don’t want to feed it. However, any new food for a rabbit, be it pellets, veggies, grass, needs to be introduced slowly. Rabbit digestion relies on healthy gut bacteria, and too much of a new food all at once can upset the balance and cause mushy poops, smaller poops, gas, bloat etc which can lead to gastro intestinal stasis, which is very bad. If she’s still eating and pooping well then she’s probably fine (If she stops eating or pooping for 12 hours, she needs to see a vet immediately), but if she seems uncomfortable or in pain, it’s possible that she’s had a bit too much of the good stuff. Give her a break from the grass for a few days and see if she picks up again. Then I would introduce the grass by just picking a small handful of it for her per day, rather than letting her free feed on it, that way she is introduced to it slowly.