What to Wear: The mask itself might be pretty easy to find, with little adaptations. Just get a wig to wear over the top of it. And, well, you may need to buy a ball gag from a sex shop. While you're there (at the sex shop), you could probably find a similar leather harness too. Then just dirty up an old dress with a similar pattern and slip on some black gloves.
How to Act: This lady hasn't done a whole lot except stand around, so I don't know what else to tell you to do.