Does she actually appear to be suffering or starving? I'm pretty sure clownfishes can smell food, as well as see it; I know mine come racing to the front of the tank as soon as their food hits the water, even if they didn't see me coming with the container. If she isn't being out-competed by her tankmates, she may do fine. You also might could try shutting off the pumps and powerheads for a few minutes and then target-feeding her some mysis or other food with a turkey baster, so it reaches her directly, much as many aquarists do with mandarins and other slow feeders.
Unless your maroon has lost her sight due to an illness, parasite, infection, etc, that will eventually prove fatal, and/or she seems to actually be in distress, I don't see any reason to euthanize her. Can you post some pictures?