Disobey Gravity

It sounds like Millie is very well-loved and protected by her climbing partner:

"Put your agenda away, be prepared to move slowly and explore the world around you at a smaller, slower pace.”

And she looks very comfortable (except in the shot with the jammed boulder, which would worry me too if I had to walk under it).

Further backstory and commentary from her human here:

My Climbing Partner Eats Chicken Liver

From the comments to the original article: Millie has climbed 5.6 multi-pitch, though apparently she required aid on certain moves.