Is it safe for my mother-in-law to live off road in the woods?

My husband and I have a small 584 sq. ft. cabin in Wisconsin just big enough for 2 people or maybe squeeze in a couple of guests. We spent several years fixing this up and looking forward to spending more time there during retirement. It is on 95 acres on a private lake and we need to cross the property of another landowner (who is only there during hunting season) to access the property. Since my mother-in-law likes nature and fishing, my husband had a small 128 square ft. building (looks like a tiny log cabin) built for her to stay and other in-laws while they were visiting us. It is a quarter mile from our cabin and has no water or electricity....it was just supposed to be a place to sleep instead of a tent. This was built about 15 years ago. However, it evolved into my mother-in-law staying at her 128 sq. place every year from May to October as it is not accessible in the winter. She decided that was her home and of course needed our cabin for water, electricity, and the bathroom. She also showed it off to her brothers and other family like it was the greatest thing in the world. We always have a lot of fun when we are all together, but I don't think she should live there on her own like she does. During the rest of the year, she lives with my brother-in-law and his wife in a very comfortable home. Our Wisconsin property is a mile off road and is accessed via a dirt road. Every year or two, storms take down trees and block the road until someone can come with a chain saw. I was there last year when that happened and she seemed a bit panicked. There is a gate to the property on the main road, but the fire dept. probably could not get through or find her. She is mentally very sharp, but tires easily and can only walk a few feet before sitting down. She needs to make several bathroom trips at night and decided to put a porta potty next to her 128 sq. ft building (about 40 to 50 fit away but I think she uses a bedside commode too). On hot days, she will sit in her car with the air conditioning on. The next thing I knew, my in-laws were putting in a propane refrigerator for her and buy her food. My in-laws never told me, but I found out for a few years now they have been doing all her laundry and taking out all her garbage. They also clean for her. The outside of this little building is cluttered with tables, bug, spray, dirty dishes, etc. She has a shot gun for protection but she is 84 years old and in marginal health. My husband agrees that she should not be there alone. My sister-in-law said it was a good time for my mother-in-law to sell her house and live with them but my sister-in-law does not seem to want to talk about my mother-in-law being on the Wisconsin property. My mother-in-law dreams about being in Wisconsin and that's all she talks about. She even calls it her lake. (The property has actually been in my own family since 1961). I talked to a nurse one time about this and she said elderly people need to feel they can be on their own. I spoke to a close relative and they said that my mother-in-law just wants to be in Wisconsin and is prepared for the end if that happens. I told my sister-in-law that I don't think my mother-in-law should be there on her own any more. The closest relative is her niece who works full time and lives 50 miles away. My brother-in-law and sister-in-law live 200 miles away. She does have a cell phone and people check on her. What are your thoughts about all of this? Should I be more aggressive as a daughter-in-law and the owner of the property? Or am I being the bad guy?