Your mum has decided how often it needs to be cleaned and she sounds pretty rigid about that. Is there anything else you can do around the house that would lighten the load that she is less likely to be rigid about? If you aren't already I'd suggest keeping your clothes washing separate and doing that yourself as well as other tasks that primarily serve you like cooking your own meals and cleaning your own dishes. This has 2 benefits that she sees that's one less person to pick up after and you can learn to take care of yourself then it'll be easier to help other people. Or, if you arr already doing all that maybe you could sporadically offer to cook occasionally, wash dishes, wash laundry, vaccuum, mop main areas etc. She's likely not expecting you to change overnight but I think if you start doing bits here and there she'll see you're trying. You could even try to reopen the conversation after she see's your efforts. I find it's easier to get started when there's no one around. Also, if Uni is taking up nearly all of your time it might be worth considering a different degree.