Operating under the theory that it is that plant, my searches didn't yield any results.
It's a relative of chamomile, which is safe for birds, so if you really want to feed the daisies to your bird, I would suggest feeding them small quantities and seeing how they look in the days following, but I really wouldn't recommend that. I couldn't find anything about rumex acetosella either. Sorry /:
I would suggest investing in some alfalfa seeds, which are relatively cheap ($4.09 US dollars here
for 4 ounces). They grow into edible sprouts in about 3-5 days and are relatively easy to grow with a mason jar and some cheesecloth. Best part is, whatever your budgies don't eat can be added in to a sandwich or a salad!
Other suggestions would be food that you eat yourself, such as (cooked) rice, broccoli, or cucumber.
I'm sure that you already knew a lot, if not all of this, but I hope I was able to help!