Could Sailor Saturn have stopped Sailor Galaxia

There is a common misconception about the last arc of Sailor Moon that Sailor Galaxia killed Sailor Saturn. However while that battle was VERY close to happening, it never actually happened. What really happened was Hotaru sensed her adopted mother Setsuna being attacked by Galaxia and flew off in a rush to help her, not even transforming, only to fly accidentally in the path of Galaxia's Star Seed Steal. 

What if an alternate reality occurred. Hotaru had transformed into Eternal Sailor Saturn before flying to Charon Castle orbiting Pluto, only to see firsthand Galaxia killing her adopted mother Sailor Pluto.

Before we figure out what would have happened let me give a quick introduction to the two fighters.

Sailor Galaxia is the Sailor Senshi of Destruction and Solitude. She is the bearer of the Saphr Crystal, the ultimate force of destruction, able to reduce things in existence back to it's primordial star seed. She is feared throughout the galaxy as the Golden Queen. Her coming heralds destruction. Merely her appearing on a planet can turn it into a barren wasteland only Sailor Senshi can survive. It is noted that the planets under her control are worlds of death where neither the living or the dead can maintain. 

Galaxia's primary attacks are Galactica Inflation, creating an aura of dark lightning around her strong enough to equal Eternal Sailor Moon's strongest attack and the even stronger Galactica Superstring creating a wave of cosmic energy powerful to threaten even Eternal Sailor Moon, which is highly impressive given the Silver Crystal of Sailor Moon is a crystal that protects and preserves, the ultimate force of life. Her ultimate attack is her most famous. By pointing at something, she can steal it's star seed, reducing it to nothing. She can do this to many entities at once, even to whole worlds. 

Beyond this Galaxia has more powers. Her power warps the spacetime continuum and can erase a future. She can hear thoughts, even so far as to hear Usagi's thought from thousands of lightyears away. She has enhanced senses, can attack the mind of her foe in their dreams, and can manipulate the star seeds in her control to recreate entities as loyal to her. 

Sailor Saturn is the Soldier of Death and Rebirth. She appears when a Chaos-Spawn would threaten the universe and resets all life to zero, such that she is referred to as the Messiah of Darkness. She is primarily a spirit, the Saturn Spirit which can incarnate a body and a soul in a time. In the Modern Era she incarnated as Hotaru Tomoe and joined with the Senshi of the Solar System. The Saturn Spirit can incarnate a new body and soul at any time, and Saturn can fight normally as merely a soul. 

Saturn wields the Silence Glaive, the scythe of death which paralyzes and harmed even Pharaoh 90 which absorbs all energy and matter. With it she can cast Death Reborn Revolution which creates dark tendrils that paralyze and draw things to be crushed inside her negative aura. However her ultimate ability is the Silence, where she lowers her silence glaive completely releasing the aforementioned "Silence". The Silence ends all life to be born again. This technique kills her, though she can cause herself to incarnate again at will. This technique was powerful enough to reduce the tau world to "nothingness".

Beyond this she has a forcefield technique called "Silent Wall" and can create a distracting mist and some form of vortex with "Silence Glaive Surprise". She also has the ability to heal.

So could the Messiah of Darkness kill the Golden Queen?

In Terms of Raw Planet Power, Sailor Galaxia would completely overpower Sailor Saturn. The Saturn Crystal is relatively powerful, but it is not as raw powerful as the Saphir Crystal, equal to the Silver Crystal. That said the Saturn Crystal is relatively hax. While Galaxia is very high in power, she has no known paralysis resistance, and the slice of the Silence Glaive or the Death Reborn Revolution should theoretically serve to kill her. She is also a lifeform. If Sailor Saturn released the silence, which she would be hesistant to do, not wanting to hurt her new Earthly friends, then it would theoretically end Galaxia's life and the Saphir Crystal would have to be reborn along with everyone else.

Sailor Galaxia's two named attacks would tear though Saturn with raw power. However they would only be able to destroy Hotaru's body. While the Golden Queen can make a world inhospitable for the living and the dead, the soul incarnated by the Saturn Spirit is particularly tough and would be able to fight on. That said Galaxia's star seed steal would remove the Saturn Crystal and one-shot Hotaru, body soul and spirit. 

Galaxia's secondary abilities would give her a massive advantage over Saturn. Galaxia's enhanced senses would allow her to see right through the Silence Glaive Surprise and it's unlikely that even the Silent Wall could stand up the power of the most destructive crystal, the Saphir Crystal (also Galaxia can literally walk through Usagi's barriers, suggesting she could do the same with Hotaru). Meanwhile Galaxia can read Saturn's thoughts, knowing her tactics. Since this is right after Galaxia took the Star Seeds of the Outer Senshi it is also completely possible for Galaxia to create the Outer Senshi to fight for her, which would force Hotaru to fight her adopted mothers, exploiting Hotaru's good nature.

The most likely scenario if Sailor Galaxia and Sailor Saturn fought is Galaxia would one-shot her with her star seed rip as that is Galaxia's preferred tactic. However if Galaxia delays, Saturn would have a chance of catching her off-guard.