I just came across your post today. Were you ever successful in your search? My grandparents/mom/etc grew up in that area - Zeibach county - and have family members from Isabel as well. I will ask my mom if she is familar with the name.
Isabel is in Dewey County and they should have that information in their archives. Zeibach County may have the information as well since many families have relatives/ancestors in both.
Let me know. Ellen