I admire your desire to see this through, and the open way you have posted here.
My wife (also in her mid 50's) had never sailed when we bough our boat, and with the boat still on the hard (out of the water) the opportunity to go for a day sail with visiting friends on their boat was exciting for her to say the least. The skipper spoke with her as we motored out on a brisk morning explaining that the boat was going to heel, but that this was normal and it would not capsize, and always come back up if it got pushed well over.
I could see her stiffen up as the sails were first trimmed on a close reach and the boat heeled to about 20 deg. or so, but she could see we were all enjoying the day so decided that this must be normal. As time went on the wind began to ease and everything got slower, and I sensed she was a bit disappointed.
A few hours later, with very little wind we were all relaxed and chatting, not really watching the sky when heavy rain suddenly hit, and, as is not uncommon in our area a very sudden gust knocked us right down, water over the ports, Genoa in the water. The boat stayed that way for about 15 or 20 seconds then came head to wind and stood up again, and just as suddenly the wind died off to about 5 knots. Nobody in the water, nobody thrown about. Poor Ruth was white as a sheet with her "I don't think I like this " expression. Our friend, always quick on his feet, immediately said, "See I told you she will always come back up"
Now Ruth knows that a keelboat can fall right on her side, but pop right back up again, and she understands that the boats' natural tendency if knocked down is to come head to wind and stand upright again. She has experienced about the worst that will happen in our sheltered area and knows it's O.K.
I won't say she wants to do it all again for fun, but she now can manage her fear.