Normally, jobs give you a maximum of 2 no call/no shows before they can you. If you have a valid reason, they can't fire you after just one nc/ns. Unless you have a history of not showing up, then they have no right to fire you.

Shift changes usually have to be approved my management. If the manager approved it, she should be the responsible and FYL. If you never got management approval than YDI.

You should have called to verify that the other person indeed showed up.

I was in the middle of something like that once. A coworker needed someone to cover her shift and I asked my sister to do it. My sister changed her mind and didn't show up. Luckily the coworker didn't get fired.

I think the responsibility relies on your coworker. Sounds though like your better off at another job. Or maybe go talk to them about it. And maybe go throw a bag of shit at your ex coworkers house. What a bitch.

Did your boss know about the swap?

This is why I always clear this sort of thing with my boss beforehand. So the burden of showing up is on the other person. YDI if you didn't do that.

so you switched a shift without consulting management? you deserved it

Any shift change at any job I had required both employees and a manager to sign off. That officially put responsibility on the person picking it up.

That's why you need paperwork to make it official otherwise it becomes he said/she said with no proof.