Basically, NC has made it possible to infer that MD colluded with Ruth from Outburst before she sent out her email because why else would Outburst be so quick off the mark to respond given how long it is since they collaborated and that there is good reason they avoid such.
It might be reasonable to infer that MD was shown it before it was sent.
That MD consipired, in effect, with Outburst and two others to engineer a useful trail of complaints to meet employment law requirements for an investigation.
This is why her response to questioning about the tee-shirt, whilst it might seem on the surface to MD as a stretch, she revealed something without realising it.
When asked if she should have been investigated her immediate reply was 'there were no complaints.' Why would that be the first thought in response? You would see that NC is trying to create a parallel and if you weren't up to your neck in BS your answer would be more likely to be: but I didn't name specific groups and attack their intergrity in public, for example
It is easy to infer that at the forefront of her mind is the advice she got re investigations that they are only really justifiable if there had been complaints.
So she go got them.