Here is the sentence again:
The comma between sister and finally illegally joins two main clauses. The first main clause begins with Kris wavered ... . The second main clause is finally Fräuleins and beer won out over modems and megabytes. To join two main clauses with a comma is to create a comma splice, a major error in sentence structure.
To fix the problem, you could use a semicolon between sister and finally. Then add a comma after finally.