I would add a slight modification to this it's some extra kino which won't hurt, before you bring up the part about there being 10,000 nerve endings in the lips you could say something like
"I want you to pinch my elbow as hard as you can"
There are barely any nerves in the skin on your elbow and you won't feel the pinch AT ALL, from there you can follow up with
"There, look it doesn't hurt, I'll show you!" *grab the skin below her elbow and give it a light squeeze, you don't want to cut her

she won't feel it anyways from there you can say "Yeah there are barely any nerve endings in that part of the arm, it's funny, it's the exact opposite of the lips, there are over 10,000 nerve endings there, the lips are very sensitive and react to the slightest touch( Ask if you can show her, if she shoots you down say something along the lines of "that's weird normal girls usually let me put my finger on their lips"), then follow on with the rest of your routine just think this would help, feel free to disregard it
