This is a good general guide to rabbit veggies! http://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/
It’s good to introduce new kinds of vegetables slowly to make sure she doesn’t have any bad reactions (gas or sticky poops). Are you feeding her any vegetables currently?
The rule of thumb seems to be about 2 cups of chopped leafy greens, a few tablespoons of starchy vegetable, and a very small amount of fruit per day per 5lbs. We often skip the starchy veggies and sometimes the fruit, but leafy greens are a staple.
For leafy vegetables, personally I feed some combination of: dandelion greens, romaine lettuce, kale, parsley, fennel, spring greens, carrot tops, arugula, mint, basil, dill, or cilantro. I buy 4-5 veggies for the week and rotate which ones I buy/feed. For Thor, who is about 5lbs, I feed her about 2 cups of leafy greens in the evening, which is enough to cover a normal sized dinner plate. I know others feed 2 or even 3 times a day, you can decide what works best for you!