Already covered it, revolver isn't going to work. Too long/heavy trigger, the hands start shaking due to nerve damage.
We're starting to think either auto 9mm or an AR after the madness is through. Although if we could be a little more positive about the reliability then the SA-20 is interesting.
-Grant
If someone is that weak they won't be able to pull back the slide on a 9mm or work the charging handle on an AR.
I've seen this in person. Lots of people with limited strength struggle to rack a slide.
Also forget about factory mil spec triggers. You'll need an aftermarket trigger for the rifle for sure.
Also why a weak person would want to carry a 6.5 - 8.5 pound gun when they could use a small revolver seems crazy.
What is the police response time in their area?
Can they shoulder a long gun long enough for police to arrive?
If response time is ten minutes it will be far easier to point a revolver. They might be too weak to keep that shotgun pointed for the full ten minutes. What happens when their arms get tired and they dip the barrel down?
Even a feeble person can open up a revolver to load and unload it. It weighs very little. You can also hold a cell phone in your other hand to call 911. You can't do that with a rifle or shotgun.
If the trigger is the only issue - get a trigger job done. The revolver is also inexpensive, easy to store safely if kids are around, and can be kept in a holster so it is handy at all times. Criminals can show up at any time. Is this person going to have an AR on a two point sling all day long?
Keep it in a holster or fanny pack with a cell phone to call for back up. If it isn't a practical thing to use it will not be handy when it is needed. An around the house gun should be in your holster. Not sitting in another room when trouble comes knocking.