If your parent is of sound mind and the house is deemed messy but not a danger to her, she can stay as long as she likes. In extreme cases where the parent does not allow any outside help and the condition of the home poses a danger, the health dept. and/or adult potective services will intervene. Will she/he allow you to hire a housekeeper or in-home caregiver to come by once a week?
Stop visiting. I rarely go into my mom's home anymore. I go into the living room (the door opens right up into it) but I cannot force her to clean, or hire someone to clean, but one thing does work: her kids won't visit her. She will clean up, somewhat, if she wants visitors.
In extreme cases where the parent does not allow any outside help and the condition of the home poses a danger, the health dept. and/or adult potective services will intervene.
Will she/he allow you to hire a housekeeper or in-home caregiver to come by once a week?