charge nurse?

hello all; new here; looking for advice; i;m a union nurse in a ccu; for the past two years my performance goals per manager was to take role as charge nurse (we switch off daily) i have been charge nurse probably three times this year; night shift charge nurse selects day shift charge nurse; yesterday i was put in charge, another co-worker came into work and said to three night nurses; (mary (our manager) doesnt want kate in charge) so assignment was switched. I was surprised; first i heard of it; so i emailed manager and asked her to validate; she emailed me back and said let;s meet and discuss.

i never have heard any feedback, pro/con, when i was in charge and was quite surprised that a coworker knew this information and shared it with others; now i;m not sure what to expect as it seems my manager must agree and i;m nervous she;s going to tell me negative things.