Perhaps have two trips out, out alone one day and a island trip together. Shame to come all this way and compromise to the point of missing out on the reef itself. The reality is to have a great snorkel and/or dive you need to tolerate a long boat trip. Islands have fringing reefs and are not barriers reefs.
Other option is to stay on an island itself but very few on the reef itself. Heron Island or Lizard Island perhaps. Quite costly.
Closer to shore are Fitzroy Island, Green island and Frankland Islands and Low Isles from PD. Much of the trip to the Frankland is on a river so very protected, island national park but not the barrier reef. Still wonderful but not the reason for the long haul trip. Visibilty on inner fringing reefs is only a few metres.Outer reef can be 15 to 40 meters. Huge difference, even if all beautiful.
Weather makes for a huge difference. Please book last minute and select low wind days. Under 10 knots your friend may not even realise she is at sea. October is probably a good month weather wise. You do not mention when you are coming. recently 25 knots, would make many sick.
Passions of Paradise is a cataraman so has more stability than other type of boat. Stops at a cay so time off the boat but also visits the outer reef. Maybe a good compromise but maybe still too much of a boat trip for your friend.