Is it possible she is overthinking the questions? I know DS8 sometimes had (and has) this problem, especially when he was in school. Often math or reading comprehension questions were very easy, so he assumed there must be something more to them (trick question? asking for something else?) and would take forever to answer a seemingly obvious question (and would then get it wrong sometimes).
I'll be watching this thread for advice. I am starting to see similar behavior with DD6 in her homework. She just can't believe they would ask her such basic questions, so she starts answering a more complex question, but then doesn't actually answer the original question!