Mabel and her mother (Headcanon)
(credit to: artemidosgif for the wonderful set!)
We see that Mabel craves to find a new path for her life, away from what her mother is and the people she hangs out with. However, Mabel continues to come back to her mother one way or another and -- presumably -- once did errands for her.
In one of the fics I'm writing I encountered this idea, and from looking at the movie it sounds very much like her mother perpetually owes Mabel and manipulates her to keep her around and coming back. Like a thorn she cannot remove. Is it because she needs Mabel around for her benefit or because she's afraid that Mabel might actually be the one to break the cycle? Or maybe it's genuine fear that Mabel may forever forget her and move on to bigger and better things without her.
We never get this explored further in the movie, but Mabel very likely wants to leave her mother behind and move on with her life but can't. Be it because she deep down inside loves her mother like any child would, or because she is afraid of leaving her little sister behind, we never even get any indication of this.
I would dare to say it is both. One is a conscious decision, not wanting to leave her sister behind. The other one is a subconscious attachment that she even seems unaware of. There is also the possibility that, like in the movie, the people who she deals with (begrudgingly) get her to come back to her mother's apartment.
It's an interesting story that I am sad the movie didn't explore more, but that's what I'm here for.