Automatically a cohost

[Webinar2]

Whenever my supervisor joins a Zoom meeting or webinar, she automatically pops in as a co-host. I have checked my settings and she has checked hers; nowhere is she listed as a default host. She also uses the same participant links as everyone else. Any thoughts on how to change this? 

[Ray_Harwood]

Are you both set up with Scheduling Privilege? 

If so, that's what's happening.  Since your supervisor has privilege to be Host of your meeting, Zoom grants them Co-Host if they join after you.  You can remove their Co-Host privilege easily enough:

If you are NOT using Scheduling Privilege, look for assignments of Alterative Host... though that would have to be done for every meeting, unless you had that in a template you used a lot.