If your mother only signed it but did not write it, it probably would not be recognized by the court as a valid Will. You could present it as evidence of her last wishes however. If there is no valid Will, the laws of intestacy apply. Take a look at the Montana laws to determine whether the result would be the same, in which case it would not be necessary to try to get this writing recognized by the probate court.
Answered on Mar 13th, 2017 at 12:33 PM