Glad to see someone else with the same issue. I've never thought about "putting on" a bit of stress as a way to calm her down. I suppose it's because they feel like they're in the wrong for being the only one who is expressing stress/excitement?
I noticed this one time when I was in college: I had come home on a break and couldn't relax, I was super stressed out and felt generally bad. I went over my best friend's house down the street, bitched to her about some small stuff that had annoyed me that day, she mirrored me and I INSTANTLY relaxed. I remember it 15 years later because it was such a marked effect.