You can carry this idea a little further. If the surname is an adjective (Like Novotny), then the female version is Novatna. If the male surname ends in "ek", like Sramek, then the "e" drops out, and the ova gets added, as you said. Sramkova. Then there's the German version. Svoboda becomes Svobodin in the feminine. This seems to be true for earlier records, at least. I have no idea what the Czech version of feminine Svoboda would be. Svobodova?