I would have to say to her, by text, today, "Received the outstanding monies for the month of September. Unfortunately, due to the delay in getting this money into my account, I am no longer extending any credit from one week to the next. You have an outstanding bill of £11 which must be paid for before close of business today. Lunches must now be paid for in advance of the order being submitted. Failure to pay for lunch before the order is submitted will result in no lunch being ordered for that team member. No exceptions.
Looking forward to seeing you tomorrow. All the best @Amelia2000"
See what happens.