I'll check Ancestry next week at the library.
There is no Nettie, or Shorter's, to be found in Ontario prior to Mabel and Ethel's arrival.
Once again you have found new info to be further investigated.
The Ellen (Clark) Shorter you found is probably the right one as she was born abt 1847. Also, William died prior to 1911 so you probably found him too.
I'll look to all the new leads you have provided this week.