My sister will not accept any help

My sister lives alone & still drives in her area of the city. She was recently diagnosed with dementia, although her daughters & I have suspected it for a long time.
She won't allow anyone into her home to help with her care except a once/month housekeeper. Yet her hygiene has suffered. She refuses to allow any of us to take her to get her hair or toenails cut, & won't do it herself. She has refused further testing to learn more about her diagnosis & how to manage it. Her daughters are concerned something bad will happen before they are able to get power of attorney to help her get placed nearer to them.
What does one do in this circumstance?