Hi Anonymous! :) Welcome to WikiTree! If you like to search WikiTree to see if there is already anyone of your family here use the search box at the top of your page. http://prntscr.com/abbs2s
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I did now for you. Put in Bertha as firstname ofcourse and Mitchell as lastname. Gave me these options: [http://www.wikitree.com/wiki/Special:SearchPerson Bertha Mitchell] Choose ofc the Bertha (Mitchell) Duckworth. Just keeping my fingers crossed now it is the one you re looking for.
P.S. I see Jane Morgan looking for same or alike answers here [http://www.wikitree.com/g2g/219239/bertha-mitchell-duckworth] at G2G