I'll start out by saying - a Wolff Spring kit, at least the trigger reset spring, can make a HUGE difference in managing the GP100 trigger. I'm a huge Ruger fan, but I abhor their factory triggers. Given appropriate TLC, even by the average gun owner, they can become VERY good triggers.
The current production standard GP100's come with Hogue grips, which are huge. The older versions came with a Lett style, wood/plastic insert paneled rubber grip. The fixed sight models came with a compact Lett Style, insert paneled rubber grip. I assume you have the full size Lett Style, and are considering the Compact.
Subjectively, yes, the compact does feel considerably smaller in hand, and is notably shorter on trigger reach. I JUST reach the trigger with the Hogue installed on an SRH (same grips for GP's and SRH's) with the "DA crease" of my finger. With the standard Lett style grips, my crease is much more comfortably placed on the trigger, and with the Compact Lett style grip, my DA crease is past the centerline of the trigger, such I have a more powerful purchase. Starting with your finger even SLIGHTLY more flexed is a big mechanical advantage. The compact is a much narrower grip, which has the disadvantage of applying the recoil to a narrower profile, but also the advantage of less bulk for your trigger finger and hand to reach around to access the trigger (see measurements below).
If recoil is an issue for her with the GP100, which it should not be, then it will get considerably worse with the Compact grip. Installed on a Ruger Alaskan, I can shoot 454C with the Hogues all day, then with the Standard Lett style grips, I'm comfortable shooting somewhere around 50rnds before I go digging in my bag for a glove. I'm not too proud to admit - I really don't like shooting more than a dozen rounds of 454C with the Compact grips, or less, without a glove. I'd rather shoot my 5" 460 S&W, or 6" .475Line with far more gross recoil than the 454C Alaskan with the Lett grips. But it IS nice and tiny, and easier to tote, and in a defensive situation where 454C is warranted, I don't envision needing a reload. 6 or less, and I'm out. As I said, that's a description of shooting these grips on a 454C Alaskan SRH, not a GP100 - it should NOT be an issue with a GP100, but consider her recoil tolerance before committing to the smaller grips.
Some objective dimensions, measured RFN on real grips, using the same SRH, and not using the most exacting of methodologies - just a mitutoyo vernier caliper, a bit of cord, and a ruler:
Min = The minimum span from the gullet at the top of the grip to the trigger (this would be effectively the span traveling from the web of the palm to the trigger finger)
Reach = The span from the midline of the trigger to the back of the grip, measured parallel to the barrel
Circumference = string line measuring from the gullet of the top of the grip around the trigger and back.
Hogue:
Min = 3.0065"
Reach = 3.2980"
Circ = 7 3/8"
Standard Lett Style:
Min = 2.7620"
Reach = 3.2950"
Circ 6 15/16"
Compact:
Min = 2.7250"
Reach = 3.2495"
Circ = 6 3/4"
So even though the horizontal spans for minimum and reach aren't much different - around 35-45thou - the circumference is 3/16" shorter on the compact. Hence, it's a lot easier to reach the trigger with the Compacts.
