As we've seen, it doesn't take very much to set Liz off and she doesn't really want to listen to anything like reason. She can be infuriated by by the need her friends have to 'betray' her by befriending someone who isn't her, royally peeved because of her (mistaken) belief that her friends are freeloading off of her, enraged by gentle chiding about her stupider habits and always, always pissed off at anyone who brings her crashing back down to reality when she's in love with being in love. To this day, she wishes that a meteor would raze Mtigwaki off the map because they didn't guide her destiny for her and also to this day, she damns the name of every man who had better things to do than to waste time on a clingy imbecile and she wishes that Jeremy had beaten April to a bloody pulp for making her feel unappreciated.
The amusing thing about all of this is that on the rare occasions that Elly takes notice of this, she has no idea in the world where Liz gets her vindictive streak and volcanic temper. After all, Elly doesn't see herself as being a raging loon who explodes at the least provocation and nurses grudges against otherwise inoffensive people who made the mistake of inconveniencing her. The same woman who sees herself as a loving, fair, firm and kind mother figure also looks back on a past wherein she was calm, tolerant and responded to life's little reverses with a cheery smile. Since she cannot seem to see that her default facial expressions are either a horrified gasp when faced with a commonplace thing she should have anticipated but didn't or a shout of irrational and violent rage when confronted with a mild irritant, she has no idea that she's mostly why Liz blows her stack over trivialities. It seems to me that it's a form of protective stupidity that allows her to sail merrily on screaming like a banshee at nothing all, safe from the knowledge that she'd have to humiliate herself by admitting that she's responsible for the less pleasant parts of her children's personalities. It's like how John is willing himself to not see that it's a lot of his and Elly's fault that Lizzie never felt as if she belonged anywhere.