It's not the volume of stuff she memorised that got her the grades, it's her speed of recall and speed of execution of the intermediate steps, calculations and symbolic transformations that can be memorised. She is smarter than me in this regard.
Usually what would happen when we would study together is she would finish the practice test first with 65% correct but be unable to answer the harder more conceptual questions at the end that required lateral thinking and deeper understanding of the topic. I would start with that question, answer it correctly then not finish the other questions in time ending up with 50% correct in total. Then I would explain to her how I answered that question and over time she gained that understanding and the ability to answer these type of questions.
When it came to the final exams I didn't finish most of the tests. I was nearly always 1 or 2 questions (out of 10 - 15 questions) short when time was up. Meanwhile she had time to finish the whole test and check her answers because she does working out faster than me and she doesn't doubt her recall, she doesn't doubt her mental arithmetic, because its correct 90% of the time. Meanwhile I'm prone to make lots of small errors and always double check as I go.
Do you see the difference? Processing speed vs lateral thinking and abstract reasoning. I learn the concepts quickly but struggle with the details, she nails the details every time but struggles with the concepts.
She would prefer to learn something by memorising the steps and then learn the concepts later (her words) while I approach things the other way around.