If you want something to be fairly aggressive, but still have an opportunity to flip, and at a decent price, I think a Storm Hy-Road might fit the bill. A polished hybrid solid/pearl coverstock, medium RG core, it won't be as hard to control on the backend as a normal pearl, but it still gives you some backend reaction. The good thing here is that pretty much anything new will be more responsive and carry better than her old Mammoth, which I guarantee is just absolutely oil soaked, tracked up, and the particles on it are worn away.
Also, some coaching to see if you can get her hand underneath the ball a little more might help also. Most people simply don't understand what hand motion actually creates rotation and hook on a bowling ball, but once you put it into terms they understand, it's definately something that can be corrected.
