Hi!!
I would start by just adding a couple leaves, and then maybe after a week of that giving your bunny a stem. Just slowly making sure your bunny’s digestion is all good with anything new. I’ve given Paisley about 3 stems every few days before, but personally I think it’s all up to how your bunny takes it. If their stool is abnormal, then I’d start to cut back on any excess. But one or two stems per day should totally be fine!
(By the way, another veggie Paisley loves is parsley. If you haven’t tried that I’d totally give it a go!)

The best veg to start out on is typically romaine. Any of the different lettuce types are great too! Try to stay away from cabbage as it can cause gas in some bunnies. Spinach and Kale are high in oxalic acid, so you’ll need to feed these sparingly. Parsley is great and my boys love it, but it can have a diuretic affect in some bunnies.

Like Tianna said, introduce veggies slowly and monitor her poops.