This is a jukugo word that uses the on'yomi readings of the kanji. You didn't learn this reading for 緩 yet, so here's a mnemonic to help you:
You've become so slow that you can only eat things out of the can (かん). You don't have the energy to cook and your arms are all loose so it doesn't even matter if you weren't moving so slowly. So just lay there, eating slowly from a can.
That waitress’ movements were really slow so she was fired.