Congratulations on your opening. Start off on the right foot and enforce your contract. Ask her to adjust (with initials) her current cheque or write a new one. Her finances are not your responsibility or business and you should not subsidize her. If you correct this issue, she will respect you and your business as opposed to thinking your rules (especially payment) are flexible. She may be wonderful otherwise, but even the nice ones are very capable of taking advantage! Good Luck