Hi David, I've been to egypt 7 times (shortest diving was 8 days, longest 3 weeks). I've done Sharm el-Sheikh and Dahab. I prefer Sharm by far, however time out to sites is between 30 and 45 mins (but on bigger boats than what I saw in Dahab, usually helps with sea-sickness).
There are 2 jettys in Sharm (Sharks bay used for Tiran, and Travco used for local - still 30 mins of boat time and Ras Mohammed). There is a third that I've used, but only for Thistlegorm, and that's a 3 hour boat ride, so I'm guessing that's not an option for you.
Most if not all hotels also offer shore dives, and the local reefs are also very nice (although I prefer the depth of the local reefs in the Shark's bay area, as it's more of a cliff with a wall vs the sandy beach bottom that I saw in Na'ama bay. I've been down to 27 meters on the local reefs, so while not quite as varied, since you are still jumping off the same pier every time, but not limited to snorkeling depth. I would suggest that you go to Sharm, and alternate as needed between taking boat days and shore days to the extent that you and your wife feel comfortable. I've attached a pic of Angelina, one of the dive boats in the sharm area - empty because there are no tourists now, but it give you an idea of the boat size in Sharm vs Dahab.
I can't speak for Hurghada or Marsa Alam, never been.
Has your wife tried using gravol to fend off the sea-sickness?