My Brooke is 10 pounds.. and I buy grass from a nursery and give it to her.
What kind of grass? Wheat grass (or rye or something similar)? I grow wheat grass for my bunns sometimes (need to buy more seeds!) and occasionally rye or some other grain grass if I find it at the local feed store. That stuff grows absurdly fast! If I remember correctly, it takes no more than a week to pre-sprout seeds, plant them and have the grass grow 6+ inches high (which is when I usually do the first cutting; I can get 2-3 before I have to start over). It's nothing like grass you find on lawns, which takes ages to grow if you're looking at feeding a bunny. I have no problems growing it and I have a really bad tendency to neglect any living thing that doesn't have a face
. Seriously, I'm BAD at plants - way too forgetful! Even I can grow wheat grass, though.
Do NOT buy wheat grass seeds or kits marketed towards pets - you'll get ripped off something fierce. You can buy grass seeds at many feed stores (sold by weight from bulk bins, so get as little or as much as you want) or online... I think I paid like $15 for 10 lbs (after shipping) when I ordered some off of Amazon about a year ago (I got ones marketed towards humans, which are the exact same thing as the kinds sold for pets but at a fraction of the price).
Wheat grass (or other grain grasses) could also be dried to make it more like hay.
Here's a site that shows you how. While I haven't actually dried wheat grass, I know the fresh stuff is FAR less prone to setting off allergies than most hay as long as you take precautions to prevent mold from growing right on top the soil (if you even use soil at all, as there are growing methods that don't use it).
Regardless of what growing method you use, it's possible to grow wheat grass without it needing sunlight (though it does seem to do better on a window sill once it sprouts), so it's very apartment-friendly. I've grown it in a closet before! You could also get grow bulbs or a flourescent-type fixture with a long grow bulb (which is like $10 at Walmart) to help it grow if a windowsill isn't available.
For a bunny the size of your girlfriend's, it's probably not feasible to grow enough to replace his entire hay intake unless you've got a LOT of extra space (since rabbits often eat their own body volume in hay a day)... however, you could still grow quite a bit without sacrificing too much space. If you end up having to go with compressed hay cubes or 100% hay pellets, growing some grass to supplement it with would help make up for some of the benefits lost by feeding hay in a compressed form (ie the long fibers).
Anyway, let us know how the hunt for a non-allergenic alternative goes! There are lots of options, so it should be possible to find a good compromise that keeps the bunny healthy without sacrificing your own health
.