You can use the workbook.get_worksheet_by_name() feature: https://xlsxwriter.readthedocs.io/workbook.html#get_worksheet_by_name
According to https://xlsxwriter.readthedocs.io/changes.html the feature has been added on May 13, 2016.
"Release 0.8.7 - May 13 2016
-Fix for issue when inserting read-only images on Windows. Issue #352.
-Added get_worksheet_by_name() method to allow the retrieval of a worksheet from a workbook via its name.
-Fixed issue where internal file creation and modification dates were in the local timezone instead of UTC."