Best I can tell 1/4 tsp is about 1.25ml, so appears you gave her 2.5x the recommended dose of .5m. I don't really know what the effects of too much benadryl in a chicken would look like, similar to a human or not. At this point I think all you can do is watch and wait. I would not give any more benadryl for sure. I would hold off on giving her water until you see how she's doing, you don't want her to aspirate into her lungs. If she starts looking better just try dipping her beak to see if she will swallow any.