There are only three reasons I can think of: 1. The family did not want to publicize her passing for whatever reason 2. The family did not want to spend the money for an obit but I thought a death notice was always no charge (?) 3. The obit was published but it was overlooked by library personnel so her name was not entered in the index
In those early newspapers, a death notice could be squeezed in anywhere and could be easily missed. Most notices for common citizens were very basic; name, date died, services from the home, friends invited.
If you had a specific date, a more thorough check of the newspapers could be done but 1900-1910 is too vague. I am reasonably sure she did not die 1908 or later.