I would go ahead and put her down. You can humanely euthanize her using the clove oil method. I am going to attach a link that describes this method.
I've had to do this for a fish when all hope is lost or when there's severe suffering. This is a link to an article written by one of our members here on AC. It is in the article forum but I'm attaching the link here for you:
http://www.aquariacentral.com/forums/showthread.php?148361-Euthanasia
Please believe me, this is a very valuable bit of information. The idea, itself, of euthanasia is upsetting and the thought of having to do this is stressful, but the method described here can be very gentle and stress free, especially for the unfortunate fish, and even for the sad human that must carry it out.
I am very grateful that I know how to do this and that I have the needed supples on hand, just in case I should need to do this at a time when the stores are closed and I have no options.
Clove oil is used, and it acts like an anesthesia, gently allowing the fish to slip into an unconscious state, then a lethal dose is slowly administered. The directions are very detailed in the article and you need to follow them precisely.
Pure clove oil is not expensive, it doesn't take much, and it can be purchased at a pharmacy or health food store. At the pharmacy, ask the pharmacist for eugenol; don't let an associate or store worker get "toothache remedy", which usually contains clove oil and other ingredients, you want pure clove oil and usually you get that from the pharmacist behind the counter.
Of course, it goes without saying that you never want to flush a fish that is dying; it is a slow death in a drain pipe lying in sludge and chemicals.
Please don't be offended by my mentioning that, I mean no harm or disrespect and I'm sure you would never do that, it's just that I always like to mention that in threads that are dealing with a dying fish.
My deepest sympathy to you over this sad situation. I have been there. I know it hurts to see your fish in this shape and it's very sad and distressful to be in the position you are in. I do feel it's too late to be able to save her at this point; euthanasia is the best course I feel. My thoughts will be with you today. Please keep us posted.