I think the best way to choose a cruise is checking the news about USPH inspections.
If a ship is lower than 90.. not recommended to go.
For example, there are some really famous ships for failing continuously and using dirty tricks to fool USPH inspectors by hiding contaminated food in crew cabins.. The worst? they were "luxury" ships.. That is the SILVERSEA cruises ships..
Disney, RCCL, Norwegian, Princess, Costa, etc.. are almost always above 90. With Disney and RCCL almost always above 95.
https://www.cruiselawnews.com/2019/...uises-ship-flunks-usph-sanitation-inspection/
On the other hand.. if she is worried about the whole petri dish. She only needs to make sure to use common sense. Like cleaning her hands constantly with the gels provided after using public stuff, restrooms and of course, restaurants.
Also Agree on planes..
I think Planes have a way higher chance to contaminate you of something. Since the thing is completely enclosed with no real full fledged purification system. Germs fly everywhere.
Plus I dont think they clean the planes very well per flight.