Do you have to be a swimmer to know how to do nautical ties?! I know how to swim, and I don't know how to do nautical ties, so I don't think there's a correlation between the two!
How do we know that she hadn't been thinking of suicide for a long time, or had thought of it in the past? She may have looked into knot-tying a long time before. I think people who commit suicide often think about it on and off for a long time - I don't think we can make an assumption that a suicide just comes out of the blue.
Here's an interesting article about suicide and Asian-Americans:
http://www.time.com/time/health/article/0,8599,1833971,00.html
Another thing: did it occur to anyone that she might have loved that little boy? Maybe it was devastating to her that he was going to die, beyond any feelings of guilt she might have had.
On another topic: I also stopped and thought about it when I read in the autopsy report that the noose was put over her hair. My first instinct is always to pull my long hair out from under anything, but I'm kind of neurotic about certain things...That did grab my attention, but then again, as someone else wrote, at that point it might not have been something she'd bother doing.