LubbockDave: I dunno man, I've had derringers and don't really consider them a viable option. As PaulS indicated, they are a contact weapon - if you have to, can't avoid or have the only choice but to put the barrel to your adversary and fire.
PaulS is verrrry accurate with his, to hit at 50 yds but that is way beyond the norm, and he may not be able to do that under stress. Again, it's fun for him to play with but I don't consider that a viable option.
You were talking about a 2 shot 9.5 oz 38 caliber - OK, it sounds good, but the grips on those things are not conducive to either easy handling or stress-fire. You can go 3.5 oz heavier for a 13 oz 5 shot Titanium 38 snubbie that you could put onto the best grips your wife could ever want to be able to handle (like pachmyers), slide that into a nice light belt holster and be one hay of a lot better off than she would be with a 2 shot.
Now, if your 6" GP 100 is a bit tooooooo long or heavy for all-day woods carry, consider having it rebarrelled to a 4" - makes for much easier packing and although not much lighter, it sure feels that way because it then becomes easier to handle, especially for your wife.
OK, this is just my opinion but please consider something a bunch more effective than a 2 shot for your wife. Having contributed my own 2 cents worth to this topic, I say HTH and good luck. Mikey.