If you want to remove "for" from your thinking, do as lago suggests above and translate "pedir" as "request." Or when you see "ask for" think "request" and then "pedir". I use the same technique for "buscar" I translate it as "seek" instead "look for". After a short time you won't even need to think about it anymore.
The "for" preposition in "ask for" is needed in English to indicate what the girl wants. See http://en.wiktionary.org/wiki/ask#Verb for examples of how "ask" is used in different contexts. You will see that, as others have suggested, "to ask for" is better thought of as "to request".
Prepositions do not always correlate between languages. For people studying foreign languages for the first time, prepositions pose many difficulties because they require people to fully understand the context for which prepositions are used in both languages (in this case, English and Spanish).
capella- I don't think that the reason is because it's redundant, but it's just not correct. Spanish and French are much alike and even in French, which is my lenguage, it isn't redundant but just a mistake. ella pide por una manzana and in French, elle demande une pomme, are the correct way to say it.
T'Nia and Mitaine, American English is also supposed to use "an" before words beginning with a vowel SOUND, such as "an hour." It sounds phoney to me if I hear American news readers and politicians use a British or European accent by saying "an historic day." (Some Americans love British accents so much, they try to copy them to seem smarter, so Brits should see this as a compliment!) :-)
Using "an" should signal a person learning English mostly for use in America that the next word uses a vowel sound. Americans say, "A history lesson, a horse, a hammer, a hidden clue," and even in the standard phonetic alphabet used by pilots worldwide, a "hotel." All have a hard "h" sound. Here we do not say "istoric." In Great Britain, France, and other countries, that may be quite common, for example saying "'ello, 'ow are you?" when greeting someone. Just as Spanish is different in Spain and other countries, so is English.
The.Other.Caleb. Thanks! Yes, it is easy to pick up the accents of other regions, even within countries. My husband remembers when he called me from the Philippines to S. Carolina in the USA. He said it's a very good thing the telephone operator assisting with the call was in California, because she almost had to act as an "interpreter" between the British-Philippine accent, and the Deep South, Southern-American-English Accent! And when I lived in California, my Southern Accent lessened, but if I chatted with my mother long-distance, my husband could tell when he got home, because I slipped back into my drawl. I love to hear regional accents, and can even detect them within my state.