This is not restricted to Swiss German. You'll find the -in ending for women all over the German-speaking world. It is a grammatical ending that turns a word into its female counterpart.
This can still be seen in modern German, although it is now only done for job titles: A female baker (Bäcker) is a "Bäckerin". A female miller (Müller) is a "Müllerin".
I suggest to use the "neutral" form "Würtz" as the LNAB, and add "Würtzin" under Other Last Name(s). Unlike some Slavic languages (Czech, Russian, etc.), German doesn't consistently inflect names.