Is my mum TA because she stopped washing my sister’s clothes and didn’t tell her?

My sister came to me and asked if Mum had intentionally stopped washing her clothes. I think it’s been a few days since Mum made this decision, and my sister said, “Well, that’s wrong. What am I meant to do now?” She feels it’s really unfair that Mum didn’t inform her about it.

Mum has been feeling overwhelmed lately because my siblings don’t help around the house. We have three dogs, and Mum looks after them all by herself, including my sister’s dog. She feeds, walks them, and picks up after them. The other two dogs tend to eat my sister’s dog’s poo, which makes it seem like she doesn’t care to clean it up since it’s not her dog.

If Mum wants my sister to do anything, she has to ask her directly; otherwise, she just doesn’t do anything to help around the house.

Yesterday, my sister cooked eggs, and when I asked if she would clean up after herself, she replied, “well I’ll eat my food first.” She did eventually clean the pan but ignored the backsplash and stove, claiming she couldn’t see anything on the backsplash and that the mess on the stove looked old.

In the bathroom my siblings share, there are water bowls for the dogs, but Mum still ends up filling them because my sister doesn’t, even though she uses that bathroom daily. When Mum asked why she hadn’t filled the water bowl one morning, which was empty and dirty, my sister said she hadn’t noticed and insisted she does fill it when it’s empty.

My sister also gets upset if Mum speaks to her in a frustrated tone and asks why she’s being addressed that way.

She’s going away for a month in December, and I believe Mum is expected to look after her dog while she’s gone.

Is it unfair that Mum stopped washing my sister’s clothes without telling her? Is there anything Mum can do to help make my sister contribute more so she’s not so overwhelmed?

TL;DR Mum stopped washing my sister’s clothes and my sister feels like it is really wrong that she wasn’t informed. My sister doesn’t help out with any tasks around the house unless she is asked.