what with her want to die but it have to be the mermaid the one who do it ? those two has nothing to do with it other ( but i guess choose to die under a beautifull girl is better eh )
I don't think she actually chose? that monster got her first and tried to eat her, but the mermaid "saved" her without her actually wanting to be saved, the mermaid just wanted to uhh protect her food i'd say :V
I think they meant at the end of chapter 2, where she decided not to just drown herself and wait a little longer for the mermaid to eat her. Just because someone's suicidal, doesn't mean they're always perfectly okay with it. Whether the issue is pain, lingering regrets, wanting to actually deal with your issues but being unable to shake the suicidal thoughts..
Sometimes, when you're depressed, you'll make excuses like this, to put it off a bit longer. She's clearly conflicted: wanting to die (it looked like because her family drowned too?) and be with them but part of her still wants a reason not to. Of course, sometimes being indecisive about being suicidal also makes you hate yourself more. Whether you think yourself a coward or just hate the indecisiveness in general. It's not a fun place to be.
That said, whether main character is eaten in the end or not, I'm fine either way. What I'm REALLY hoping for is some realistic, sympathetic looks at how people can struggle with, cope, and possibly overcome mental issues. A bad or stereotyped portrayal would probably kill this for me.