D.A.
The only thing I have to tell you is that our children learn how to treat people by watching us. Several years ago it became apparent that my father in law could not live on his own anymore. My husband has a brother and sister within 10 minutes of us and because of his father's past behavior and messiness none of his children wanted to take him. I told my husband that we had to take him in; we have a large home, our child was off in college and my husband is retired so he is home a lot. He lived with us for about 2 years before he passed away and even though I did not enjoy having him in my home I would make the same decision. My husband and I have a farm and we have cottages and such on it. When my father retired I wanted my parents to live near me - we hadn't lived in the same state for 20 years. My husband agreed that they could live here on our farm. My hope is that one day, if I need my daughter's help she will be there for us. I know that one of my aunts treated my grandmother horribly and now her children treat her the same way - and she wonders where they learned this behavior.
I know that your situation is different - you have children at home - and between taking care of your family, house and possibly working you sometimes just can't handle the additional pressure of having her around. Maybe you could ask her to sit outside (when it is nice out) and watch the children play, ask her to bathe them, maybe if you ask her to do things around your home she will either turn out to be a huge help or maybe she will decide she doesn't need to come over quite so often. I would just be careful how I speak about her and treat her in front of your children. Good luck!