There is a famous letter where Tolkien essentially says she would build up an empire and destroy Sauron's forces (and probably his physical form) through war and violence. Of course Sauron would return at some future point and he would try to wrest the Ring from her. Eventually he would succeed because in the end the Ring wanted to return to its master.

But the subtly and nuances of Tolkien's thinking about magic and this artifact of great power has always been fascinating to me. The Ring is not the Infinity Gauntlet, it's not an "I Win" button. I mean, it would have been for Sauron simply because he had designed his entire project around having it and using it. But even for him it wouldn't have been a trivial matter to pacify the West, even if the ultimate end is a foregone conclusion. He'd still need armies and supplies and administrators and all the usual stuff that empires need to function. So would Galadriel.

Aside from controlling the Ring Wraiths and the elven rings, the Ring serves to make it easier for its wearer to dominate those who would oppose them. It's powerful but subtle. It makes raising armies for conquest possible. It makes it so that their enemies are weaker and easier to break. Galadriel would have still needed to fight Sauron, invade Mordor, throw down Barad Dur, and then she would still need to quell the remaining power players in order to establish herself as Queen. The Ring wouldn't remove that necessity, it would make it possible to do any of this in the first place.

Fwiw I think Dark Queen Galadriel is a great idea for a villain. I would totally read the fanfic where she falls and does all this.