The way I heard it went down was that William was the lead, naturally, and William gathered them up to leave and was saying to them all something like "let's head out..." then Meghan interjected with some sort of "idea," supposedly suggesting that they switch sides and each work the other half of the crowd, and Kate shot her that look essentially communicating to Meghan that she needed to shut up and do as she's told.
A lot went down BEFORE they appeared. Meghan had Netflix crews there and was attempting do a walk about with just her and Harry ahead of William and Catherine.
The palace/W&K got word and palace security put up a perimeter moving Netflix out of range to film Meghan, summoned Harry and Meghan and said if they wanted to do the walk about it was happening right then or the two of them would not be participating at all.
Meghan was preparing herself for a grand solo walk about appearance at this time, and so when they called her out and said that her plans had been thwarted, she had not yet finished spackling her face orange and combing out her wig. She expressed her frustration because she didn't have time to get dressed up like a whore to mourn with people truly grieving outside. They basically said shut up and get in the car, if she wanted to go because otherwise she would not be allowed to greet the public in any other walkabout basically ever again in her life. She and Harry were both "briefed" (to me it sounds like they read them the riot act) that they were to follow instructions, not make s scene, etc. So after all that, when Meg piped up and interrupted Will as he was telling them all that they would be leaving, Kate had basically had it and glared her into shutting up.
The irony is that Meghan looks so much better without the ghastly make up and hair sacrificed from the scalps of hundreds of Midnight Shimmer My Little Ponies. She looks very mouse-y, but she looks pretty with the more natural look. Being natural is, however, anathema to Meghan and all she stands for, so she looks like a shipwreck most of the time.