L.A.
I don't think your niece has any legal right to the property. Kansas Law states for succession,
"K.S.A 59-508. No spouse, child, issue, or parents. If the decedent leaves no surviving spouse, child, issue, or parents, the respective shares of his or her property which would have passed to the parents, had both of them been living, shall pass to the heirs of such parents respectively (excluding their respective spouses), the same as it would have passed had such parents owned it in equal shares and died intestate at the time of his or her death; but if either of said parents left no such heirs, then and in that event his or her property shall pass to the living heirs of the other parent."
In other words, the estate goes to the deceased's siblings. If you live in Kansas, you should call the sheriff's office to have her removed and have the locks changed to the property immediately. You also need to call a probate attorney. The niece is not a blood relative, and if there is no will, she is trespassing and stealing.