she can have a veggie now.  usually at about 3 months actually.  start off with something simple like a dark green lettuce or herb like parsley or cilantro.  try to give it everyday for a week, and then each week or every other week adding a new one.  it’s recommended that they get about 2 cups of fresh veggies a day… you can start out less than that and work your way up as you add more and mroe veggies.  eventually you’ll wan ther eating at least 3 or 4 different veggies a day to add up to 2 cups.  some veggies you need to be mroe careful with than others b/c they may cause gas or are too high in calcium.

here’s the Binky Bunny veggie list… https://binkybunny.com/Default.aspx?tabid=144

and the HRS veggie list… http://www.rabbit.org/care/veggies.html

i’d suggest printing out a copy and taking it with you to the store.  i know if i don’t have a list i tend to forget things easily.  you might also want to check it off if you try a veggie and he likes it so you’ll remember next time.

edited to add:  on a related note, as she gets older and is getting mroe veggies, you will be able to decrease her pellets (timothy pellets if you’re not feeding them already) to betw/ 1/4 and 1/2 a cup a day depending on her weight.  ask your vet for their opinion on this too, of course.

my bun is only 3 months and gets on fine with most veggies, he likes parsley and ive found it easy on his tummy, just remember to start with tiny amounts because too much will give him poopy butt!
see the list above which beka has given you for what you can give!