I took my sister helmet shopping the other day, and after exhausting the stock of three decent shops, we had to give up!
We tried lids from Box, HJC, Aria, Schoei. Shark... full face, flip front... all in S or XS, they all fitted fine around the cheeks, but she could still 'nod' her head fairly easily with the helmet held still.
Is there such a thing as a company that makes tailor fitted lids? Or is there another brand I've missed that might fit better? The only alternative I can think of is to get the best fitting helmet we can find, and just live with the up/down movement - she'll ''only'' be a pillion (I know, terrible attitude, but...)