Don’t let go of your fan theories yet!
I reckon she is part of the red lotus, here’s why
• Suyin seemed take her sweet time hid behind the rock to put the metal around P’Li’s head (maybe deciding between helping her sister or team mate?)
• The way she pushes Lin out of the way to make sure she’s the one to get the poison out
• The hesitation in her face like ‘I can’t believe I’m having to do this’
• She could have left some poison in Korra which is why she’s not healed after two weeks (?)
• The resemblance to Zaheer in her circus photo is pretty close if not exact
• Kuvira (the metal clan captain) looks like an exact mix between Suyin and Zaheer (could be their child)
Also on a side note, how awesome was it to have Zelda Williams do the voice for Kuvira?!
Your theory is sported.