Partners You Can’t Trust

We had to do a major project in physics. I was partnered with this pretty hardworking girl, so I thought I could trust her to hold up her end of the project. It was easiest for us to divide the work in half. I showed up the next class with all of my 2 hours worth of my project and she had nothing. I have to lose a lot of points because she didn’t do her work. Why can’t I have a partner I can trust? Plus, it’s my grade, not hers, so I should only have to be responsible for my own work.