Hi Julie,
Congratulations! Like Chris, Mary and Michele, I also have donated to charity auctions. I think it's a good way to get your name out there in the community.
I just wanted to add that it helps to have actual portrait samples to show clients when they are contemplating a portrait. (This means having them on display when your client comes to you, or bringing a painting or two when you visit the client.) Generally, people have a hard time visualizing what a real painting is like. You may have a portfolio of photographs of your work, too, but nothing beats the physical presence of real art. This is a good argument for spending one's free time painting family members and keeping them around for a while. (The paintings, not the family members.
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Let us know how this commission goes. Have confidence that you can make your client look wonderful and you'll transmit this zeal to her at your meeting. You'll do fine!