Back in high-school, my friends and I would play card games inside during recess and everyone else who needed help would come to us as we had the highest marks. It became problematic when some students wanted us to do the work then and there, but one of my friends thought of a beautiful idea. We often wanted money in order to give them our services, so once we got the money, my friend would write bullshit answers. For example, for math homework, he'd make the answers believable by doing some of it correctly but then intentionally adding something incorrect that made the overall answer wrong. People hated the fact they gave us money and we gave them bullshit but it didn't take long for people to simply ask us for help (which we were willing provided money) rather than do the work for them.
I also would screw others who I didn't like just before tests. I'd be sneaky and take their pens and pencils, then dump them somewhere, however, I always carried a large set of my own. Naturally they'd ask me for a pen so I'd hand them a pen that had very little ink in it so if lucky, they could write a sentence or two. Again, things don't come free from me so I always asked for money. Those who I liked, I'd give them working pens usually for a discount or free, just to further screw with all the others.
Sounds childish because well, it is but it also works. If you want, after you've correctly done your homework, do another copy that's incorrect and have her copy it. Once she sees her mark is crap and may blame you, then you show her you got a high mark (C isn't high but it's better than a F).