Of all of Wildbow's shitty retcon's Canary's is probably the least offensive.
We see several powers in canon increase in potency during high stress situations. So her power managing to apply her master effect by just shouting when confronted by her abusive ex who has somehow gotten past her security seems pretty reasonable. She had to be extremely stressed and her power could have picked up on that.
While it's a stretch it's not a large one.
Unfortunately that's not what the retcon is about. This wasn't a case of extreme emotions empowering an ability, this was her power activating without her prompt or knowledge. Basically just leaking out without being noticed. Which is why I call it power incontinence. If such a phenomenon was known to people, then parahumans would be much, much more careful because you could never know when it happens to you.
Paige never mentions any security and since she was just starting to play at larger venues and didn't even have a contract with a label yet, she might not have had a full crew around her. Or maybe she's an unreliable narrator since she's telling this story to Bakuda after being threatened, while waking up from sedatives on her way to the Birdcage.