A little more poking into past discussions shows that Bonnie B. Burke = Bonnie Beatrice Garrison, daughter of William S. Garrison, who lived in Lucas County, Iowa in 1910 and Indianola, Warren, Iowa in 1915. Is that right?
1910 William Garrison 43 Emma E Garrison 40 Merle F Garrison 15 Bonnie B Garrison 12 John F Garrison 9 Leo C Garrison 3 Fred H Garrison 0
In seeking Bonnie's marriage certificate, her location in various years is highly relevant.
You might write to the county where Bonnie died for a copy of her death certificate. You know her death date and married name, so you should have good luck obtaining a copy, and usually death certificates are not terribly expensive. An online transcription, if found, probably won't list all the information available on the original death certificate (such as the name of the informant).
I've looked for obits and will try some more searching - or maybe some other volunteer will come up with those. Hope so!