I think I understand what she's saying. The blue arrows don't demonstrate water flow, I think she's using them as a "pointer" to indicate which way the valve points.
Is the black cylinder inline with the white pipe in the lower right corner of the bottom two images a check valve, and if so, is it possible that that valve has failed, hence the spa draining into the pool through the returns?
I have a similar problem, except I don't have any check valves in my system - I've been contemplating adding one or more.
You could experiment by running the pump in "pool mode" for a bit until the spa starts to overflow, then put the valve marked "Spa Operation" into the opposite setting as it is pictured, shutting the pump off immediately after closing it. If the spa doesn't drain, I'd think that was your problem.
Edit - to be clear, I'm suggesting that you put all valves into "pool operation", run the pump, let the spa overflow, then just turn the valve labeled "spa operation" to the opposite side as it is pictured in the spa operation image - which should cut off all water flow to the spa return, putting all water through the pool returns. Then shut off the pump. If that is a check valve, and it's bad, having that valve shutting off the spa return line should verify if the problem is with the spa return line.
