Try adding the following code between sheet = workbook.active and # Create dataframe.

for r in list(sheet.merged_cells.ranges):
    cl,rl,ch,rh = r.bounds
    sheet.unmerge_cells(str(r))
    for i in range(cl, ch + 1):
        sheet.cell(row = rl, column = i).value = sheet.cell(rl, cl).value