hmm, having been a facepainter, pre-children, i will now try thinking about it from a SN pov!
dd2 (likely AS) hates, hates, hates the tickliness.
she can't even bear to have her fingertips painted for finger painting.
but she would dearly love to have her face painted, i reckon (as in, she would love to be a tiger/princess/whatever)
is there anything you could do with just your fingers? maybe a butterfly in glitter gel? less tickly, for sure.
agree with Goblinchild that small designs, in case of waiting too long/not able to bear too much painting.
so details form your designs, really - quick 2 minute jobs on a cheek.
sponges are much better than brushes, imo.
what designs are you going to do? you might be better off working out 4 or 5 that you can do either full face or with small details, so that you aren't caught out with a child asking for, eg spiderman (god I used to hate doing that web!) and not being able to tolerate that much tickling.