Honest question: Where was Becca in SS Babysitter's Island?

[BRONTE]

I'm confused about something; where was Becca in the Super Special Babysitters' Island? Some of the chapters have her participating in the boating/sailing race with Claudia and Dawn whilst being shipwrecked with them, and other chapters mention that she's home alone with Squirt being watched by Jesse while their parents were on a second honeymoon of sorts; only to get caught by her Aunt Cecelia. Was she in two places at once somehow or was it a writer's goof? Where was she in reality? Did she actually participate in the race with Claudia and Dawn or was she at home alone with her sister much to Aunt Cecelia's dismay? 
Which one was it?