Most children don't realize that they have to "over learn" something to get the new information into one's long-term memory. I suggest that a child study new information frequently and review often. For instance, if your daughter has vocabulary words to learn, put the words and their definitions on 3x5 cards, which have been cut in half to allow for more cards to use --- word on one side and definition on the back. Band these or use a one inch ring, so she can keep them all together. Ask her to review them while she is waiting for the bus, in line for lunch, before class begins, etc. It's better to have several mini-review sessions than one long one.
Before your child sits down to read her academic books, ask her to fold a sheet of notebook paper in half like a hot dog. Ask her to look over the section of the chapter she is about to read. Have her look at the subtitles and then on the left side of her paper, ask her to write a question(s) that she expects could be answered in reading that section. Do this for all subtitles. Include unknown vocabulary too. For instance, she might write, "What is industrialism?" She should look at all the pictures, charts, etc. These alone will yield a lot of information. Before she begins, she could even look at the discussion questions at the end of the section, if available. Finally, as she reads, ask her to write the answers to her questions on the right side of her folded paper. When she is through, she will have a ready-made study guide for her use.
I suspect your child may be a slow reader who reads every word rather than the center of lines. In the beginning try to sit down with her every other night and read the class work with her. You can vary this by taking turns reading paragraphs or by reading one night while she listens and then visa versa. After each paragraph, stop and talk about the important information within the reading. This should help to build a stronger relationship between the two of you as well as building her reading skills.
Even when reading a fiction book, especially if it is needed for a report, ask her to keep a reading "diary" of each chapter read. She will need to stop and think about what the main character did or what happened in that chapter. Some students do well by sketching a picture to represent the chapter read along with the short diary passage. A small spiral or a writing notebook is a good tool for these exercises.
Encourage your daughter to read anything and everything. Just read --- soup labels, road signs, comics, news headlines, etc.