I suppose it's good to have a taste of what real contractions will feel like. I don't think I'll be misidentifying them - if they're happening regularly, I will definitely notice.

Mmm, flavoured chalk. I stocked up on Tums while I was in the States so I have a little supply to carry around with me. When I'm at home, I use Gaviscon, which tends to banish it straightaway. Best of luck to your sister-in-law!