Hermine Bittner (Hoffmann) - Marie (Mizzi) Thausing

My grandmothers full name was Bertha Maria (Mizzi) Thausing, nee Konrad, first husband Hugo Bittner, with whom she had a daughter: Anny Thausing-Bittner, my mother. Her second husband was Friedrich Thausing.

... but nobody called her Bertha, she was generally known as "Mizzi".

As far as I know, Hugo Bittner was only married to my grandmother, Bertha Maria Thausing, nee Konrad, widowed Bittner, re-married to Friedrich Thausing.
Marie nee Bittner does not make any sense, especially since her birth- and death dates are identical with my grandmother's.
My mother, Anny Thausing-Bittner was born May 6, 1912.
Hugo Bittner, my grandfather, died in 1921. My grandmother remarried in 1923.