I haven't read all this thread yet - nothing after your post so may repeat what others have said - but could she have put something into the kayak through the hole, which would have affected its ability to float, or to remain upright, or keep it steady? I'm not sure what, but is there something in a power or crystal form, which when mixed with water could solidify and then affect the balance? Probably too far fetched, as she must have realised that his kayak would be found/searched.
I find the scenario of people watching through a telescope a bit odd - especially with her asking to use it some time later to look for his body. Was she trying to establish exactly what they could have seen that night? And how did she know they had a telescope? If she knew them (and the fact they had a telescope set up to view that stretch of the water) before the night in question, why choose an area you knew might be under observation if you were going to commit a murder- unless she was setting herself up some witnesses, but failed to convince them that she was trying to save him.