Birthing a new fictional character

I'm usually percolating a novel for quite a while before I start writing it. Currently I'm editing a completed novel, eager to get back to a started novel, and beginning to think about a future novel.

In a recent post, Expectations and Disappointments and Novels, I discussed tripping across an idea for a new novel. The idea would be that not every beautiful, desirable, or useful thing will live up to our expectations. Often when we least expect it, something (or someone) will be a huge disappointment.

I happened to run across a woman the other day who fired my imagination. She was a drive-thru bank teller. Our interaction was brief--I deposited a rebate check, and she cashed it.

When the envelope with the cash was returned to me I stuffed it into my purse and went about my business. Later I noticed she'd written a message on the back of the envelope:

Note that she wrote the message in purple ink and highlighted it in pink ink. Then she signed it and stamped a smily face.

And when I got home and opened the envelope I found she had put a shiny star on the receipt.

A day later I had lunch with a friend and showed her the envelope and receipt. We decided that this teller must be the happiest, most optimistic person or she surely has too much time on her hands.

This might not seem like much, but it's the beginning of a personality for my main character. So far she's a content, happy, and optimistic person who has led a charmed life. That's until . . .

And that part I haven't figured out yet.