That is poor communication and inconsiderate on her part, but you could have just explained your situation to her and asked her how you could come to a reasonable solution. I don't think being passive aggressive is going to help your working life go more easily. Not knowing all the details, it feels like you felt taken advantage of but are playing the victim instead of having the maturity to realize that not everyone sees things from your point of view but that doesn't mean they are bad. Speak up and ask for what you think you need. Be prepared to have a conversation about it.

Your MB is a jerk. But that said, if you agreed to swap days, you agreed to swap days. You don't get paid extra. If you agreed to work an extra day, and then she told you AFTER you worked it they it was a "swap" then she needs to pay.

I get it.

You were entitled to Wednesday's pay since your agreement states that even if you are not needed to work that day, then you are still entitled to guaranteed pay anyway.

So since you weren't needed that day, you are entitled to that day's pay.
And so whatever hours she asks you for on Friday, these are to be add'l extra hours which should be paid for as well.

So you are entitled to your regular Monday-Thursday guaranteed weekly pay PLUS the extra pay for working on Friday.

She sounds like she is hustling you because she has zero right to switch days around on you if you already agreed to guaranteed weekly hours.

Take the advice others gave u and move on. Focus your energy in finding a new position. Take care.