There does seem to be a dearth of information on Holke. I'm guessing it's one of those Germano-Slav names (wish I had a less clumsy description for them). The -ke ending is a regular feature of German surnames of Slavic origin, i.e., Hubke, Jerschke, Jobke, Krupke. As for the meaning, I'm tempted to associate it with a Czech name that was discussed on the list a few weeks ago, Holyk. The meaning of this name was ambiguous, but something like bald, or shaven, or hairless. I have found a Sorbian place name, Hola, which is known officially by the German name Haide. So Holke might be based on a place name.