Grrr I'm so mad at myself...lesson learned! Plus, awkward situation.

[apples and bananas]

I think it's wonderful that you will see them frequently. It gives you ample opportunity to address the issue with them in person. " I never did recieve that cheque you were going to send me, I was concerned it got lost in the mail, but I couldn't get a hold of you? Is everything ok? " lol

Make her uncomfortable. You can be the nice person who was concerned that there was something wrong... and keep confronting her about it. At every event! Money is money no matter how big or little. Make sure she understands that you've not forgoten about it and don't intend to.