... her counciler said it will be good for her to come here for a while and learn to get back on a routine of eating, taking showers and maybe learning to cook.

It sounds as if your niece's visit will be more than just a casual weekend venture. I'm a bit pressed for time at the moment but link I'll recommend to you is this one. It might give you some additional ideas for creating a healing environment that can facilitate recovery: The Windhorse Project: Recovering from Psychosis at Home. There may be some ideas there you can adapt to your own home environment. For example, learning the practice of basic attendance can help create a calm and stress-free environment for you and your niece.

The founder of that project also has a book that may be of interest to you, your sister and your niece: Recovering Sanity: A Compassionate Approach to Understanding and Treating Psychosis. In addition, if you click on my user name it will take you to my profile. I have three photo albums there, one of which features books I've found helpful for understanding and moving on from this experience. You might find something else there that will be helpful to you.

I love my niece and will do anything for her.

It's very kind of you to be willing to take her into your home for a period of time in an attempt to help guide her recovery. Social support is critical to recovery, especially support from the relationships that have the most significance in our lives. If those relationships are loving relationships, that's all the better.

More thoughts later as time permits but I thought I would leave you with that link/book recommendation for now.

~ Namaste