Turns out something did actually happen: Rusty got hurt! But this happens so often in Mark Trail that it may as well be nothing.
Actually, I'm pretty sure that Sassy's finally had enough, and that this whole beach trip thing is a plot to finally get Rusty out of her life. Unfortunately for her, of course, nobody gets away with this kind of villainy in Lost Forest. I look forward to the image of Mark Trail punching his young ward's puppy in the face.