Maybe, but she was still very social and had a lot of (what she considered) fun, went womart hoardeen, luncheen with friends. Got her nails done, wore her hair down. She may have been heartbroken over Destiny, but she was still living an active life.
I think there were many straws (warping the expression should be allowed given amber's size). Leaving her job and staying home all day meant she had no reason to get up, get ready, or participate in hangouts after work with coworkers like she used to. Part of her relationship breakdown with destiny was probably due to the fact that she was no longer a fun, people person. She never wanted to go out with destiny and have fun (as opposed to go out mainly to have food).
I think the main, main straw was just Becky. Becky is like a fog of gloom, and add that to amber's general gloomy outlook. Amber no longer had to pretend to be fun anymore, because low-energy becky wasn't fun. They were both fine to color, watch movies, play games and not socialize at all. I'm sure there are places even in their backwoods areas where they could go to make some friends, but they seem content to have nobody but each other. Isolation has brought out the worst in Amber (which is something because interactive amber was pretty shitty too), and she's no longer fighting her slovenly ways, and there's no reason to shower or do her hair or anything. So circling back, quitting her job was the first step in no longer having to be presentable on the regular, or interactive.