If you cannot solve a problem, look at the solution. Do not just copy it. Analyze the first step. Ask yourself: "Why did they divide by 2 here?" or "Why did they move the variable to the left side?" Close the book and try to replicate that single step on your own.
By midnight, she had solved not just Problem 87, but 88, 89, and 90. The logic no longer felt like magic. It felt like a language she was beginning to speak.