There's some information missing here. How long would the last 23 miles take for you to finish? 2 hours? 3? Was weather getting worse? How about wind? Was that last part of the course tougher than the earlier stretch?
You did say you were the LAST rider out on the course. Typically it can be hard to get volunteers for a charity event. Even harder if the impression is that people sat around for 2+ hours in the rain because there was 1 rider left on the road.
It seems like the communication could have been handled differently so that you would come away feeling better about the situation. Would you have felt differently if the organizer met you on the course, exlained the situation, offered a refund, and then called the event?
I'd chalk it up to experience and move on. If I had to vote. I'm on the side of the organizer. She lost 1 rider for next year's event, but kept all of her volunteers.