Over her life, my wife has had several ruptured eardrums from bad colds, and she is afraid to learn to dive. She probably could do it, especially given one of those special masks with the ear equalizing devices, but I learned decades ago not to push things like this. Fortunately, she loves to snorkel, and she loves being on boats. When we go on trips, she looks for the best options for herself.
Here are some examples.
Often its the "I'll dive in the morning; we'll do something together in the afternoon" plan. During the dive portion of the day, she willl often do something that she will enjoy more than I would, thus sparing me from an ordeal that usually includes shopping. (I would rather have my eyeballs pierced.) Often she will arrange a snorkeling expedition of some sort. When we were in Belize earlier this year and in St. Maarten the year before, for example, she even took full day sailing/snorkeling trips that she really enjoyed.
Other times the boat trips I take will include reasonable snorkeling. When we were in San Carlos, she and the non-diving friends who accompanied us snorkeled with the sea lions while I was diving not that far below. She will snorkel from the boat pretty much any time she is told the snorkeling is mediocre or above. She even went to Bonaire with me and did almost all of the boat dives and even some of the shore dives.
When we were in Australia, she signed us up (she handles the travel arrangements) for a four day liveaboard trip on the outer edge of the Great Barrier Reef. She intended it as a very nice gift to me, but it turned out to be the highlight of the trip for her. The GBR actually breaks the surface in places 60 miles off shore, and it was the greatest snorkeling she has ever had. I think she was in the water more than I was. On the last dive of the trip, my buddy and I were milking it for all we were worth, and we ended up using most of the last breaths in our tanks near the very top of the reef. My wife was snorkeling roughly 5 feet away from us when a minke whale passed by, almost within touching distance. That was a pretty nice shared experience.