This website has some cool dialect stuff:
http://accent.gmu.edu/browse_language.php?function=find&language=english I honestly feel that the best way to learn an accent is by listening to it. Veruca should probably have quite a posh accent because she's wealthy and spoiled-- so I'd recommend watching period films. I did "Pride and Prejudice" a few years ago, and I watched the numerous film versions over and over again. Now I can do a weird spot-on impersonation of Keira Knightley (even though I wasn't playing Elizabeth!) If you're playing Veruca, try to copy the accents of young people in period films, not older people, because their accents tend to be more affected and old-fashioned.
You can also do a slightly more modern accent, for which I'd recommend listening to Emma Watson in Harry Potter. There are some noticeable differences in the vowels.
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy