Sorry, Armor951 beat me to the post but at least I am on the right track.

This is just a guess but is there any buildup on the face of the cylinder or face of the forcing cone? Next time bring a toothbrush and brass brush and clean the cylinder front and back when this condition starts to manifest itself to see if it helps. If you have a very tight barrel/cylinder gap that may be the source of your problem. There are other potential possibilities but they are above my pay grade.

As far as the trigger weight of pull, you have options.
1. Thousands of dry fires may help (something that always seemed silly to me) but it will strengthen her trigger finger.
2. Install a Wolff spring kit which will reduce the felt trigger pull and make the gun much more controllable and enjoyable to shoot.
3. Take it to a gunsmith and have it done professionally which in the long run probably makes the most sense as they can also accurately diagnose your original issue. If you are planning on keeping this gun the cost of this service amortized over the life of this gun is tiny and the benefits are enormous.

Others will chime in with a better answer to your "difficult trigger pull" but I would still consider doing trigger work, especially if it is for your wife.