Why it's called a curveball--I might never know. Using a 4 seam FB grip, think about pulling down the front of the ball at release--kind of like a flip change in fastpitch. I wouldn't focus on the bend in the elbow--just pull the lower arm/ball into release with the body, shoulder and upper arm. Sequence is everything...
Oops! Sorry! I was thinking baseball!
For the rollover, start by moving the ring finger tip to the stripe and releasing off of it. To take a little speed off, whip the thumb down the front of the ball at release. If it helps, try releasing off of the pinky.
Still not close to where it was. She will throw 2 or 3 that are pretty dang good but it just doesn't look natural. What do you teach as far as release point?
Teaching a release point is a fallacy. You will hear it often..."Release a little sooner" or "Release a little later" and so on. Ridiculous advice. Think about it. You are asking a pitcher to make an adjustment of literally millimeters within a time period of literally milliseconds.
The only way to "teach" a release point, on any pitch, is the same way you teach location....repetition, repetition, repetition and after that.....more repetition. The athletes mind and body will eventually synchronize for the desired result.
Outside of the macro scope of brush triggered release, there is no way to "teach" fine tuning a release point.
Going back to earlier in the thread, I'll just reiterate the point that you are really much better off just going with a peel drop over a rollover drop. Just my opinion, but it is easier to throw, easier to control, and has less of injury. Rollovers will tend to contort the pitching motion.