I could see her staying on the court even through Obama's first term, but when he won his reelection, that was the time.
And that's not just hindsight either, there was plenty of discussion about it.
Of course there's also the issue of McConnell's shitty stunt in the Garland nomination (and the reverse shitty stunt for Barrett) and I will celebrate the day that piece of shit dies for those, but the first year of Obama's second term would have been plenty of time to get it done.
But yeah, in a just world, a senator from Kentucky deciding for the entire country that he's going to go against his constitutional duty and refuse to take up the Garland nomination for a year and a half?
That's when he's dragged out off the Senate floor, out onto the capital lawn, and hanged for attempting a coup.
After that's done, everybody goes back inside and whoever is the backup Senate majority leader is asked to take up the nomination. At that point it's unlikely they refuse.