That doesn't follow, logically.
"It's impossible to swim to safety" does not equal "I want to die". At best, it equals "I'll probably die", which only means she preferred the off chance of something unlikely happening to the alternative; NOT that she intentionally WANTED to die.
It's like jumping out of the Xth-floor window of a burning building. Sure you'll PROBABLY die anyway, and it's unlikely you'll ever survive a fall like that; but not impossible. That doesn't mean you're committing suicide, you're just taking a chance on a very very slim outcome because the alternative is worse to you.