What made the woman nervous?

M: Are you looking forward to your trip to Canada, Julie?
W: I can’t wait to see Canada, Jack. We can’t agree on how to make the journey. My husband insists on flying, but I want to sail. Planes make me nervous.
M: There is nothing to be frightened of. How many planes fly across the Atlantic everyday?
W: I have no idea. Hundreds, I suppose.
M: And how often do you hear of a plane crash? Once or twice a year?
W: Yes, but planes fly so high and so fast that once would be enough.
M: Look, there are more people killed in road accidents every day than in air crashes every year.
W: I’d still prefer to go by sea. Ships may not travel fast but at least you can relax.
M: It’s fine if you’re a good sailor, but have you ever traveled far in a rough sea?
W: No, I’ve only been in a boat once. I sailed down the River Thames for sightseeing, but I’d rather be seasick than dead.