I agree with your DP. It must be tricky with two, but they do learn not to run off in the majority of cases. I'd try teaching her that first before the meet and see how you go. Start small, somewhere where you can keep an eye on her and spend the time reinforcing your message.

This is from a mother whose DD would not sit in the pram from 12 mths as she wanted to walk. waaaay before she understood how to control the power of freedom! LOL