I have roots in the Czech Republic also, predominantly from formerly German speaking parts. The Czech feminine forms of the names were not used in the many documents I have found. By the way, my family always considered themselves Austrian, and not Czech, as the country was the Austro-Hungarian Empire when they lived there.
I have a few contemporary documents, and also extracts of church records made in the 1930s. These documents are often bilingual. Czech feminine forms of surnames are never used in any of these. When I compared these to the archival records, names were exactly as used in the archives.