Nutrition questions. PLZ HELP

So I realized the other day that there were some long green plants in my rabbits cage. I knew my sister had been weeding up some long green plants from our garden, and thought she was maybe giving them to the rabbits. I went to my mom and sister and asked them to plz stop, because they don't like them too much, and my one rabbit just pees on them and then they stink. Turns out, that it wasn't the green plants I thought it was, they were leeks. My mom had put some left over leeks in there cage. I saw for myself my rabbits eat some of the leeks and since leeks are part of the onion and garlic family, I was wondering if I should get them checked out. I don't think it affected them much, but I know onions are horrible for them, so I can't help but worry.

Also, my rabbit Mistletoe has been losing a lot of weight recently, and I can't figure out why. She seems to have almost shrunk. This has also happened before. I was thinking about feeding her a different diet that should put some more meat on her bones, but am slightly concerned. I don't think it is a big deal, and can be easily fixed, but I thought I would get some ideas. Thanks!!!!