Esther might find it a great relief to be able to consider Lawrie an ass, I think; feeling generally incompetent at life herself (which she isn't, but I don't think she sees it that way) and being surrounded by the variously competent and confident Nicola, Miranda, and Tim, she might find it reassuring to have someone else around who is obviously an ass at times, whether through incompetence at practical things, saying the wrong thing out loud, etc. (I'm sorry, that was a ridiculously long sentence.)
A side effect of this discussion has been an unshakeable image of an older Lawrie cast as a gender-swapped Dogberry, perhaps momentarily harking back to that moment as she complains "Oh that I had been written down an ass!"