My daughter's reading score on the ACT was poor. She has a tough time not being thorough. We are working on skimming - a needed skill for this part of the ACT.
I don't know that "skimming" is necessarily a skill needed to excel on the ACT reading - but fluency and speed are certainly helpful, as is rapidly retrieving details from the passage and drawing inferences from them. Have you done a diagnostic practice test to see which particular kinds of questions she is missing? Targeted practice on those types of questions (and lots and lots of practice tests, with an emphasis on her weak sections) can often help make the most of test prep time.
My son has more trouble with the "social inference" kind of reading questions than with anything else - not surprisingly. His strategy on tests like these is to go through and answer everything he can answer within 10 seconds of reading the question (marking down the number and giving his best quick guess on the others just to have a "place-holder" answer so he doesn't have to remember to fill in the next answer leaving a skipped space), and then going back to "actually" answer those he has to really think about if he has time at the end. This can often be helpful if time considerations are an issue - no point in running out of time and missing easy questions at the end because you felt compelled to answer all of the questions in order.
I don't see the current SAT and ACT as necessarily correlating at extraordinary levels with IQ. For the most part, they test skills that can be explicitly taught more than pure reasoning ability, and, due to the time constraints, reward good working memory and processing speed as much as they do straight reasoning power.
