She now knows what Horgan's word is worth.
The Greens threatened to topple government a few times and stood in the way of $10/day childcare and easier access to unions. Horgan didn't want to steer through a year of uncertainty with a shaky foundation, you really need to let this go that it was all a power grab.
Also, Horgan made a deal with Andrew Weaver's Green Party. Weaver has left the Greens and has gone on to endorse Horgan. That alone speaks volumes.