Despite what you read in the newspapers about shark attacks, people snorkel throughout the caribbean and never see a shark. After 11 cruises and 30 or more snorkel trips I finally saw my first shark in the water in Grand Cayman and it was a docile nurse shark. Not to worry .
See, two serious answers , we are very nice folks when we know the question is serious.
I am a certified diver and I asked my instructor the same question. He told me NO, because that is "dead" blood. and is being washed from the body. Sharks are attracted to fresh blood. So tell her not to worry.
What about jewelry? I've heard that shiny objects will also attract sharks. I have a light necklace with two charms on it that I never take off but in Puerto Vallarta last spring I was advised by my group to take it off. But two ladies also had their periods and were advised not to go snorkeling. Now I am hearing differently on that subject. But, I will listen to the dive intructors advise. He's the expert!
I'm with you Barb, don't want to cause any unnecessary attention!
Don't know for sure about sharks but barracuda definately are attracted to shiney objects and have been know to attack and bite at them. Yes it is wise to remove jewelry before diving. I forgot once and noticed a very large barracuda eyeing me with way more interest than I wanted. I promptly placed my hand behind me out of his sight and left the water. As for the normal female cycles, again a tampon will keep any problems from occuring and in most cases just a good as well as hygenic idea anyway.
Confirm barracuda's attraction to shiny things. Also disconcerning to find one (usually very large) taking advantage of the shadow of your boat. If you see a shark while diving in the Caribbean is will probably be a nurse shark. Harmless, even friendly, but will still scare the hell out you the first time you encounter one. Get a photo, good for stories.