They also revealed another potential motive in the show, in addition to the insurance: that he wanted to call off their engagement. But I am still stuck on how she could have flipped his kayak. Or, as you said, did he capsize on his own and she just took advantage? The whole flipping herself out when the rescue boat came is just so hinky.
That one is easy. She'd be hard pressed to flip his boat on perfectly still water with his consent, and even then the odds are she'd flip herself instead.
On wind-waved waters moving downstream at a good clip, mid-stream, her own dexterity reduced by cold (no wetsuits, mitts/gloves), and both paddling without skirts (water coming in = more difficult to control)? Not just unlikely, but close to impossible.
As for throwing herself in, capsizing herself. One cannot readily throw oneself into white water from a kayak. It is theoretically possible she deliberately capsized her kayak, but to know that with any degree of confidence a witness would have to be very close by.
She could just as easily flipped at a time only later thought odd because of other cues. She also was unprepared and unqualified to be on the river that day, given the conditions. I'm surprised, frankly, that she didn't die too.
edited to change thought about the impossibility of tossing oneself into white water from a kayak. Typically one tries to remain IN, and though I've stood my kayak on end in holes (enders) and gone over waterfalls and run big water backwards, all for fun, it occurs to me it never occurred to me to try throwing myself overboard, so to speak.
Sit on the floor, legs fully extended in front of you, and imagine you are sitting in a kayak; the cockpit, a full 360 oval, comes up to your waist, and you're getting tossed around by waves.
Getting out on purpose? Squirmy, awkward,,difficult, and definitely obvious.