How many office supply orders were made by Cindy Stewart in the south superstore?
office supply refers to Category = 'Office Supplies'
SELECT COUNT(*) FROM south_superstore AS T1 INNER JOIN people AS T2 ON T1.`Customer ID` = T2.`Customer ID` INNER JOIN product AS T3 ON T3.`Product ID` = T1.`Product ID` WHERE T3.Category = 'Office Supplies' AND T2.`Customer Name` = 'Cindy Stewart'