Hard to tell but looks like the red mark might be a scrape?
Agree with other points brought up. I'll also add - it could have been the stress that caused the bite, a 'just leave me be', it could also have been something totally accidental that you didn't notice happen (said you were talking to your friend at the time?). I rewatched a video I had taken handling one of my ATBs that had bitten me and at the time I thought it was just normal ATB bitey behavior but watching the vid back I saw where my fingers accidentally pinched her by the neck for just a second and that is what caused the bite. Possibly something got pinched or moved weirdly when you were at home and taking her out that last time. Or she had simply had enough.
Good luck with the mite treatments, be vigilant and use PAM as directed.