Personally, I think you looking for something to handle medium-dry is to big a range to have one ball try to handle. A medium shot could be medium in length but not in volume. Or long in length and not so much volume. Dry is dry and with enough surface, hand, or slow enough ball speed anything can and will hook on dry. I would say look into picking up 2 bowling balls. One for med, and another for the dry. A lot of the balls stated will work well on med and some better for the dry. If she doesnt have alot of hand but is still throwing the ball 14-15 mph, dont be scared to look into something like a vibe or freeze or even a 607A or burst, or from outside ebonite international, a victory road or python. I have sold alot of 607As to some older guys in my area who bowl on old wood lanes who throw the ball 14-15mph with slightly below ave rev rate who play it up 10 all day every day and score just fine.

 

Yet to ask one ball to cover medium oil to dry lanes is just to hard to pull off. What ever ball you get, would end up shinning better on one of he conditions then the other and that will lead to miss use of a ball due to a lack in confidence on one of those conditions.