Denna's friendly... so I normally let her go ahead and meet people. I do often ask people to wait, and have her sit, first. I also will ask kids that are shy if they'd like to give her a treat, and then show them how to do it (open palm)... when they go after a pat on the head and Denna jerks away, I try and show them how to scratch under her chin, which is less intimidating (for the dog!).
If it's someone I don't want to meet, or Denna doesn't take kindly too, I just tell them, 'sorry, she's in a bad mood today (or not feeling well)', and we walk away.