バチ (罰)means "punishment", あたる(当たる) means "hit" or "strike". Verb in te-form + ほしい (欲しい) means "want that [verb] happens". わ is a kind of particle that doesn't really have that much meaning (a bit like "well" in English) and is mostly used by women. Put together, the literal translation is "I want that punishment hits you", but don't use that, it's just for explanation.
I personally prefer be a little liberal with the literal meaning where necessary. Many literal translations of Japanese phrases may make some sense in English, but let's be honest - how likely would you be to hear someone say "I want you to be struck with retribution"?
As Serizawa posted, I would go with something along the lines of "I want you to pay for it/that/everything you've done", depending on whatever it is the speaker wants her target to recieve punishment for.