Manager of groups stopped appearing as member and groups stopped appearing in her "my groups" list
Apparently the user was still manager of her groups, but was no longer registered as a member. I was able to use the Masquerade module to assume her identity, go to the appropriate node/%/group menus for each one she was manager of and give her membership again. Everything seems to be back in line after that. My guess is it was caused by overzealous use of an alternate link/rule-set I was experimenting with to manage group enrollments/drops. I've now disabled that until I figure out how to get to function properly.