Thanks very much for your help. (I have not yet reached the point where I automatically think of Google.)

There appear to be at least three different verses/songs mentioning Frau Wirtin. The one I meant is the one at Frigger's Humorige Seiten. It is probably the oldest. I am disappointed that it seems not to have been set to music.

The usual translation of "Frau Wirtin" is "the Innkeeper's Wife". I gather that it was a common situation for a married couple to run an inn together, and they were called Wirt & Wirtin.

Sad to say, I know too little German to understand the many stanzas given at the site, without some dictionary work.