Yep ulcers are an issue with gouramies. There are some treatments you could try if that's what it is but it looks quite far gone in that pic and dwarfs don't handle the stress very well anyway so she'd more than likely die in the end (and forcing her to suffer through a treatment that probably won't do anything for her is unfair).
How much clove oil you need can depend a lot on the fish, the amount of tank water it's in and so on... There is no exact guide but what I'd suggest you do (besides searching the beginner's forum and emergency forum as I think there are a few posts concerning this sort of thing there) is get a bowlful of tank water, net her and put her in and then start adding, little by little (it doesn't usualy take much at all though gouramies, as they can breathe air, sometimes take a little more). Try a spoonful at first. I actualy use a syringe (without the needle obviously) for this so I don't know the exact amount and I just add until the fish is obviously gone. Watch carefuly as many fish appear dead but are simply unconscious. The gills have to stop moving. With gouramies, you don't need to freeze. If you leave an unconscious gourami underwater long enough it'll drown anyway. If you want to be on the safe side, do the whole procedure, then leave the fish in the clove oil for an hour or two (freezing a conscious fish is extremely inhumane - if the gourami is still moving in any way, add more clove oil and keep it in there longer) and then freeze until the top of the bowl has a thin layer of ice forming on it. At this point the fish is deffinately dead. Destroying the brain is still reccomended (even after all this) but it's not realy necessary.
RIP little gourami. I'm very sorry for you and her but it's for the best.
Red 
