The Woman in Cabin 10

This is a mystery. It features the most helpless and stupid protagonist I've ever come across. Lo Blacklock suffers from anxiety and panic attacks. Also, she's a bit of a drunk. She works for a travel magazine. When her boss becomes too ill, Lo gets a break and joins a little over a dozen others for the maiden voyage of a smallish luxury cruiseship that has ten guest cabins. Then something sinister happens, Lo is stirred from her drunken stupor, eventually tells people what she thinks. They don't believe her. She sucks at her job too. She doesn't really have much going for her. I stuck around to see how the central mystery wraps up. I had guessed right a little past the halfway mark. I might've muttered “Just die already” to the main character at one point. No luck.