There is a certain time / point in your life which makes you realise "duck it, lifes too short to feel like this / tolerate this" etc and its different for everyone. It might be a loveless relationship, an abusive one, it might just be the realisation of coping alone with said children who all have different needs and paces. You try to keep up a persona to deal with it and eventually you learn its beyond your abilities and the support you need just isn't there.
I don't think she's a bad mam, I think she's just a human, embracing her situation of 3 ferrel kids whilst keeping a bit of her sanity and seeing the funny side in life. What would you like her to do instead if swear? Video herself standing in the shower, crying having a breakdown and ignoring the kids battering on the door for her attention? I swear infront of my kids but they are firmly told you don't copy what you see, it's only words at the end of the day, they will hear them from peers and other people and I'd rather they learned they aren't taboo but just not for children to use.