Among all the orders made by Aimee Bixby, what was the longest shipment time?
made by Aimee Bixby refers to "Customer Name" = 'Aimee Bixby'; longest shipment time refers to MAX(SUM(SUTRACT(julianday("Ship Date"), julianday("Order Date")), 1))
SELECT MAX(strftime('%J', `Ship Date`) - strftime('%J', `Order Date`)) AS longestTimeDays FROM people AS T1 INNER JOIN central_superstore AS T2 ON T1.`Customer ID` = T2.`Customer ID` WHERE T1.`Customer Name` = 'Aimee Bixby'