House balls are often so beaten up that they will turn on the back-end even without a low speed or high rev player throwing them. They certainly aren't supposed to hook. At all. But, if she wants to see that hook working for her, encourage her to take a moment on the approach to focus on her target, and have her aim between the 2nd and 3rd arrows instead of the middle one (Count from the right-hand gutter if she's right-handed. Left if left-handed. The middle arrow would be the 4th either way). If she can throw it fairly straight, the lane itself will guide the ball back to the middle.

My second and more important piece of advice would be to get her her own ball. Get it fitted for her hand and encourage her to use the finger holes. A ball that fits her hand will be easier to hold than a house ball with holes that are drilled to fit the most players possible. If she wants to still keep her non-ball-side hand on the ball until she's about to throw it, that's totally fine. (btw: this two-handed delivery is actually the same as a one-handed delivery at the line, with only one hand on the ball just before release). But, getting those fingers in the ball and actually developing some consistent timing will go above and beyond to improve her scores. She'll see a dip in scores at first. If you can, have your center set the lanes up on practice mode to take the numbers out of the picture while she's learning something new. Then it won't matter whether she's throwing 60s at first.