Could be something for high enough WIS considering it's one way she can escape from the Woodsons or could be an additional trait Nympho and timid personalities can get
Also she's smart enough to build a raft to escape the fishman and willing to suck up the abuse going along with her captors demands long enough to try and recover
Although it could also be argued developing Stockholm syndrome is a symptom of stupidity and weakness seeing the shitty treatment of your captors as desirable and this is shown with Nympho Lona seeming to have fun being abused (especially with the masochist trait)
Stockholm syndrome should be something tragic and pathetic with your confidence tied to pleasing your abusers and in turn abusing those you see as weaker than you even if she'd be the most pathetic and weak minded of them all maybe even getting the happy buff for pleasing her captors
Plus it would be VERY fucked up if the easy way to survive relatively speaking was staying with some group like the Woodsons because it was easier to stay with them instead of surviving on your own