The Grease Monkey's cover will fit for what you need.  I would not drill it the same way you currently have your Crossroad.  I would put a control layout for her to smooth out the back ends for her when the lanes begin to dry up.   

Tim,
What do you consider to be a "controlled drilling."

The Lt 48 seems to be smooth and arc rather than long and strong. Look at some videos of it or at the PBA league finals where one of the bowlers used it quite a bit even after the heads were toast.

If her speed is 10-11 at the pins then her speed off her hand is around 13mph.  This would mean she is well on the slow side of average.  Bowlers with slower ball speed usually do better with lower differential balls on average house conditions, especially when the lanes break down.  The Grease Monkey is an excellent ball but unless her rev rate is very low, she has a lot of tilt, or the lanes are very slick the Grease Monkey may be a little early for her to see a large difference between it and the crossroads.  Better options as mentioned may be a lower differential ball like the LT 48 with a smoother reaction or maybe a Ringer or Misfit Pearl if her style lends its self to the ball rolling very soon.  A number of women bowlers I have had experience with tend to have very low tilt and axis rotation.  This tends to lead to having the ball roll out too soon as the lanes start to get drier rather than the ball running away from them.  It is usually better to have your proshop guy evaluate and decide between the above options as he or she probably knows the intricacies of your wifes game better than we do.