I went with a marionette style mouth, with replacement mouths. I decided to blend the lines in TVPaint afterwards, as it seemed the most efficient way to go - both pieces of the head are baked and I didn't want to start getting plasticine crumbs on her sweater. Here's the video of her talking:
I also finished another 15 sec of a puppet doing exercises (pushups and stepping in place) but sadly the small versions are on my laptop, which I am now without for the next week or two. On the upside I've only got 6 days to finish off 3 more sculpts, 10 castings, and alot of sewing for another project so no laptop is probably a good thing!!