Yesterday, it got warm enough to work in the garage comfortably W/O heat so I got to work.
First the order of business was to strip off the grip and twist shifter. (The Mirrycle mirror was borrowed from my bike to previously check compatibility with the bars)
The brake lever was removed to allow the SRAM X4 thumb shifter to slide onto the bars and then replaced.
Next, the grips were slid onto the bars with some soapy water as a lubricant. After making up a new piece of housing and routing the cable, the shifter was adjusted for flawless, easy shifting. The shiny new Mirrycle mirror was installed in the handle bar end.
IMO this is a huge improvement over the twist shifter. The SRAM uses thumb actuation for both up and down shifting and is much better for tiny fingers than a trigger shifter.
Finally, the Sunlite Derailleur guard was installed. It required a flat washer as a spacer under the bracket to allow clearance when the derailleur is in the smallest cog. Without the washer, the cage was just touching the derailleur.
There is yet one requirement left on the granddaughter's must have list. I need to order a side loading bottle cage. Thus one is available for $10 shipped on Amazon.