I saw Patti in concert in Pittsburgh a few months ago. After the performance there were probably about 75 people waiting outside afterwards by the stage door. The security guards had us form a line and come into the stage door and file past her as she signed things. She politely ignored any requests for photos, and they kept the line moving very quickly, but she was polite and very friendly/nice. I think she just likes respect and wants to get to everyone. If all 75 people wanted to stand there and ramble on about how much they love her and stop her to pose for a picture, it would take forever to get through everyone.
Being that this is a benefit, she might have obligations to appear at a reception, etc. (if there is one) after her performance. She might not stage door because of this.
If you DO decide to stage door, it might help you to "blend in" a bit more if you dress up and make it LOOK as if you were just in the benefit concert.
If she does sign, don't expect much more than her quickly signing one (maybe! two things) saying "Thank You" and then moving on to the next person. Let us know how it goes!
"I'm seeing the LuPone in Key West later this week. I'm hoping for great vocals and some sort of insane breakdown..." - BenjaminNicholas2