First of all, love makes you do crazy things, and she knew that if he was gonna die on that ship, then she was gonna go with him. "You jump, I jump, remember?" Of course she didn't in the end.... but she had no idea at that moment what was going to come. Second, she was a rich woman who had probably never used an axe before. Women back in 1912 didn't have a reason to use an axe, expecially if they were rich. She aimed, and she missed. Not on purpose. More of ignorance that stupidity. Yes, she was ignorant. Not her fault though. Third, She was desperate to escape. She wanted so bad to get out of her life that she was willing to commit suicide. People who commit suicide are not stupid, they just don't have a way out. Fourth, I would have done the same thing. What was she suppose to do say "Yes, I have the million dollar necklace, but you can't have it, because I'm gonna throw it in the ocean." If they didn't attack her, harrass her, or anything else, they would have gone back down as soon as she was gone. They were treasure hunters. And she was giving the Heart of the Ocean to the ocean in his memory, and I thought that was so sweet. She was so in love with him. Rose was not stupid. Granted, she was ignorant, but she was a girl, no not a woman, a girl, in love with someone who just happened to die. Of course, this is just my opinion. it's really up to you what you want to believe.