Whom should be used to refer to the object of a verb or preposition. When in doubt, try this simple trick: If you can replace the word with “he”' or “'she,” use who. If you can replace it with “him” or “her,” use whom. Who should be used to refer to the subject of a sentence.
Help her white out the old grade and write a new, better grade on it. However, it would only be positive peer pressure if the best friend reads up on the subject first.