give her a valium next time.
better living through chemistry.

I'm going to vote on the closet rods or banister handrail wood.  If you wanted to create some pockets using PVC fittings you could run the rod over the gunwales of the canoe and then use a "T" to get a right angle off your float and then another "90" to get an opening in the correct direction for the wood to pocket into.

I use a PVC "T" to make attach my boom on my sailing canoe to my mast.  BTW my spars are wooden closet rod and my mast is a wooden banister:



I included this particular picture to illustrate that if you were to have her sit on the floor of the canoe on a thin pad the canoe would be vitually immune to capsizing.  In this pic above I have 40 sq. ft. of sail area I am counterbalancing by just sitting to one side of the canoe.  If the wind lets up I don't roll because I'm still within the canoe's "base of support" (not the correct term).  The canoe will tip but it's very easy to counteract by leaning to the center again.

So to answer your initial qustion.  PVC sucks as a structural material if it has any sort of load on it.  If you don't believe me you can check out the clothes line supports my father in law made from 4" PVC.  By the time he was done preventing sagging he had it braced with wires like a combination of a power pole and a WW I biplane.