Drk.Pch, I'm going to give you the best advice that was given to me....well as far as both the depression, which I suffer from and also Peach.
Depression- Keep yourself busy, and do stuff that's fun and not frustrating. I can't stress this enough. Hang out with people you KNOW will make you feel better. 'nuff said. Trust me on this one.
Peach- The best advice that was given to me, when you practice, DON'T use peach, use someone else. That improved my peach SUBSTANTIALLY. Now all I have to do is work on being faster. Another thing might be your controller. For god sakes....the wrong controller will kill your game. I let Reik borrow my controller that I broke in to my liking and went out and got one....kinda similar for the last tournament. That made a huge dent in my game. (At the same time though....the controller I gave to Reik was in better hands, lol.) Anyway, I played this Marth with the "other" controller and lost. I played him again with mine and was beating him....like badly, too. I don't know what was wrong, but a controller makes a difference, too. Try these two things, and try to be open minded about choosing another character to practice with. I use Roy, though he's low....low tier. I also use Y. Link....I just started, I guess I wanted to see why VaNz liked him so much. Y. Link is fun, to say the least. Also...he has the down b that pulls out bombs, very similar to who....? Get used to doing things with other characters aside from Peach....it'll make your Peach better. Had I have known that my controller made THAT much of a difference I would have used it in the first tournament I went to. Might have gotten me further. Now I use the new one I got, as a handicap of sorts. I know I can go all out when I use my real one.