Omg I did this once - honestly felt like my lungs were on bleeping fire, but couldn't stop as there were people behind me horrific!500 steps is quite intense. To be honest I'm shocked she even tried it so good on her. I convinced myself one day I could walk up the Covent garden tube steps which I think is about 200. Needless to say I was breathing out my arse and have never done it again since.
I can understand the concern for Callie, but you can't be concerned and then blast her for doing the activity that will *help* her if she continues to do it. Lockdown fucked up my fitness big time, and one of the things that stops me from doing stuff is the high level panic that people will hear me getting out of breath and judge me big time. Fair play to her, she's doing the steps, she is sounding out of breath on stories, she's not dodging it - I admire her for that tbh.