That play sounds great! It would definitely be interesting to see them meet on the show. It's so sad that Elizabeth could not be persuaded to meet with Mary in real life.
ETA: Leaving this here because if you click on the video at the bottom, Ade talks about how close she and Rachel are and how she would love to work with her... but she doesn't think it will happen because Elizabeth and Mary never met in real life.
http://zap2it.com/2016/04/reign-seas...serial-killer/