Here's what I think happened -- Sharon Bush wanted to get back at the Bush family in a public way. And meeting with Kitty Kelley for a public luncheon was a way to put the family on notice that she was a loose cannon. And both Sharon and Kitty both agree that Kitty was the one to bring up the "Bush did coke at Camp David" allegation. I think Sharon agreed with Kitty about it; heck, at that point, Sharon was so angry with the Bush family that she would have agreed with allegations that W was a space alien!
Anyhow, the divorce between Sharon and Neil Bush was finalized after this meeting, and I would guess that there was a "keep your mouth" shut clause inserted into the agreement. But at any rate, the damage was done. It is curious that Kitty didn't take notes during this lunch, nor did she tape the conversation. It seems like Kelley just wanted to claim that a Bush family member confirmed her wacky allegations.