I agree with much of what Foggy posts. However my mother (who was blind) went on our boats with us, including two of our trips to AK, when she was in her late 80s. We made sure that there were plenty of hand holds, and supervised her going up and down the companionway ladder (more like a stair case). Our aft stateroom in the Cal 46 had our queen sized bunk on one side and a settee which made into upper and lower bunks on the starboard side. We had her sleep in the lower bunk, which was "sitting distance" from the floor. She went with us a few years later on the Symbol Sundeck, aft cabin "trawler"--she slept in the forward cabin, but we always helped her in and out of the bunk She also rode in our 20' Grady White walk around while she was in her early to mid 90's.
I am 87 and am having problems with boarding and climbing ladders and this is why we gave up the last C Dory 25. My advice is to be sure that there are good hand holds available, preferably on both sides of the gunnel. For example a Bimini with SS 1" pipe which is solidly fixed both fore and aft, as is in the Tom Cat 255 in my album, below; note that the SS pipe is well secured fore and aft to the deck, not a railing or thin aluminum tubing.
I have added handicap handrails on the pilings holding up our boat lift on the shore side. I can bring the gunnel near to the dock/deck level. That way, I can use the hand grip, plus there are two "boxes" built in about 15" above the deck on the Caracal Cat, and one can step on the gunnel, then down about 12" to the "box", and we have a folding step which is 8" high, so to that next.
For the C Dory 22, you should bring the boat as close to a gunnel height at the dock, or above the gunnel, so your mother could easily step to the gunnel, then to a solid box, and folding type of step, with you and another on both sides to give her balance. She should be sitting all of the time when underway. Talk her through the procedure and see if she feels comfortable.
Another good way is to have the C Dory 22 gunnel 15 to 16 inches above the dock and then have her sit on the gunnel and pivot her feet into the cockpit, and then she can slide down to a stool, or sturdy storage box before stepping onto the aft deck in your 22. Again, have someone on each side if her for strength and stability.