My first question is why do you want to change to a lighter arrow? If she is currently shooting ACC's and they are spined right for her bow you are not going to find a better arrow period. Switching to a lighter broad head will do nothing but change the spine and FOC of your arrow. You will not notice a difference in speed. Maybe on a chrono, but not in actual shooting, especially with a set up that lite.

If you are looking for speed I wouldn't bother too much because with that set up you are not going to see much anyway. No matter what you do it will still be slow in comparison to the average set up. Those are a bit stiff for that set up, if you could find some that closer matched they might be a bit lighter. I don't think being a bit stiff will hurt anything though, just adds more weight.

I come up with 327 for 3-18's at 24 inches with 4 inch vanes and a 100 grn tip. You could use easton jazz arrows with feathers and be around 350 grns and by three times the arrows. You could drop your tip weight and switch to feathers, that would cut your weight down if that is really what you want. I highly doubt you will notice a difference without a chrono though. And if you are looking for pass thrus on deer I would be looking at heavier arrows with cut to tip heads.

Just my opinion, but I shoot a lighter set up. Not that light, but light enough that it is a concern for me.

Paul