If a person can take off her mask when shaking one person's hand but have to wear her mask to shake the other person. That is already pretty much show this is a deliberate act. I think to use being sick as an excuse to try to diverge attention is both very low and lame.
Respect goes two ways and if one do not respect the principal why expect the principal to respect her.
Please do not find any more excuses for this shameful act.