Never saw the Filoni take, yet I'm guessing this massacre is Mothma's outing (open defiance), and no turning back point?
I don't feel Mothma looked bad in R1, from what I recall, they were talking about disbanding, committing the full alliance force to this one suicide mission and open war, was dividing and pulling the council apart, and it would out them. (for some Draven had already crossed a line attacking an imperial base).
And though she might be willing, it was pretty much a sacrifice she couldn't
ask others to make.
On the other hand, that's exactly what Andor and his click of self described. "Spies, Saboteurs, Assassins" were already doing, ready and willing to sacrifice themselves on a possible suicide mission.
Nobody had to
ask it from them.
It's what Luthen imbued in them.
She then (despite the Council's trepidation) conspires with Organa, to go ahead with it all...
Witch transmits to what the Rebellion is knowingly willing to do, on a glimmer of hope.