Abandoned Sith Temple, Classified Location, 3638 BBY, Old Republic Era.
A lone woman clad in black and dark charcoal grey robes stood in the centre of a long abandoned and ruined Sith temple her arms extended in front of her, her palms facing upward. Her deep red hair swayed in the slight breeze. The most disturbing aspect of her appearance were her eyes for they were a deep unnatural yellow. She was projecting a force containment field around the Sith artefact several meters in front of her calling on all her strength and power in the Dark Side to do so however she was tiring and wouldn't be able to maintain the field much longer.
The scream of ion engines made her look up briefly as she saw a familiar Fury-class heavy interceptor make for orbit and safety. She smiled her friends, allies and loved ones were safe and that's all that mattered. The woman frowned at the misbehaving Sith artefact and wondered why she'd been sent to investigate this. A dark chuckle passed her lips. She had to admit assassination by Sith artefact was original. Better than an idiot trying to drop a mountain on her head at least.
"May the Force serve me well." She murmured as she released the containment field. The Sith artefact now free to complete the task it was made for did just that and in a blinding flash of light Nathrrya Palatine, heiress of the ancient and noble house Palatine of the Sith Empire, Darth Avarice Dark Lord of the Sith and Empire's Wrath disappeared.
Hogwarts School of witchcraft and wizardry August 1992
The great hall of Hogwarts was empty as the new school year would not start for some weeks yet. In a blinding flash of light a red haired woman in dark robes appeared she swayed on her feet then collapsed unconscious she would not wake for several hours.
It took much to surprise Hogwarts for the sentient magical castle had seen and experienced much in the past thousand years but it would be safe to say that Hogwarts was very much surprised at the sudden appearance of the mysterious red haired woman within the great hall. Due to the wards that protected the castle it should not have been possible but Hogwarts could not deny the physical proof.
Hogwarts should have informed Headmaster Albus Dumbledore of the intruder but Hogwarts was not happy with the headmaster's actions and hadn't been for sometime so she felt no pressing need to tell him anything. She had become deeply concerned in the past year by the headmaster's actions regarding two of her students Harry Potter and Hermione Granger. The sentient castle was thinking it was time Dumbledore stepped down as headmaster but as yet hadn't found a suitable replacement. Minerva McGonagall was a possibility but she was an effective deputy and it would be a shame to lose her in that position. After all it was Minerva who actually ran the school.
Using her magic the castle carefully entered the mind of her unconscious guest and almost instantly Hogwarts encountered very impressive passive mental shields which she gently worked her way past. The castle was in no doubt that if the woman was awake then she'd be dealing with strong active shields as well. Hogwarts spent some time looking through the woman's thoughts and memories and what she found surprised her. Her unexpected guest was a very strong and powerful dark witch. But dark did not mean evil. Hogwarts saw that the woman lived by a code of honour that had been severally tested by a terrible act of betrayal but had come out stronger for it. The woman was a warrior through and through for she'd fought in a galactic war that had raged for six years.
Hogwarts saw the events that lead up to the woman's sudden and dramatic appearance in the great hall. She had willingly scarified herself to ensure that those she considered friends and family had time to escape the trap they'd been lured into. The woman had expected to die a warrior's death instead fate and other ideas and had sent her here to Hogwarts. The sentient magical castle withdrew from the woman's mind and considered what she should do next. An idea formed within the mind of Hogwarts she would wait for her guest to awaken and go from there.
Again this is as far as I got. I had the vague idea that Dumbles makes the mistake of trying legilimency on Nat and he pays the price which leads Nat to becoming the new headmistress of Hogwarts. This then leads to all sorts of interesting developments as it's Harry and Co's seconded year.