Thank you for any possible help.
Homework usually relates to material that a student has just covered in class, and it relies on short-term memory. But a test can cover material that a student might not have focused on for days or even weeks. Also, students are required to do more higher-order thinking on tests: to synthesize information, draw conclusions, make comparisons. So, a test can be more demanding than a homework assignment since it requires longer-term information recall and critical thinking skills. Add to this the fact that taking a test can be a stressful experience for many kids, and it's understandable that tests are difficult.
But parents can help their kids learn to prepare for and take tests more effectively. Your friend can sit down with her daughter and go over each graded test to look at mistakes and pinpoint problems. Once the child becomes more aware of her thinking processes, she is on her way to improving. Your friend can also talk to the teachers to find out if they have insights or suggestions.
Your friend would be wise to work with her daughter to build these skills now, before she faces the demands of high school.