Ashildr (Doctor Who)

Ashildr, who later began calling herself Me due to her immortality-related memory loss, was a Viking girl encountered by the Twelfth Doctor and Clara Oswald. After a battle with the Mire, Ashildr died, but she was resurrected by the Doctor via a Mire repair kit. As a result of this, Ashildr became immortal. She went on to live a long life, becoming very experienced and familiar with the universe and its various species in the process. Ultimately, she lived through the remainder of human history and to the end of time itself, and in the process, managed to outlive every other immortal in existence.

Ashildr lived to the end of the universe, maintaining a reality bubble to keep her alive. She then boarded a TARDIS stolen by the Doctor, and watched silently as Clara wiped the Doctor's memories of ever travelling with her. She and Clara then took the Doctor to Nevada, disguising the TARDIS as an American diner where Clara pretended to be a waitress. After Clara realised that the Doctor's memories of her were fully gone, she and Ashildr left Earth to travel the universe.

Abilities:

Due to the Mire technology within her, Ashildr was functionally immortal, which meant she did not age, injuries and illness that would have killed a normal human would heal, and she had a potentially infinite lifespan. There were limitations: according to the Doctor she was not totally indestructible and it was possible for her to be injured sufficiently enough to die. She also suffered from memory loss over time, as her human brain was incapable of storing millennia's worth of experiences. For a time, she relied on volumes of written diaries to remind her of events from the past. (TV: The Woman Who Lived)

During her time as mayor of the trap street in London, Me had a mental link with an agent of the Quantum Shade that manifested itself as an animated tattoo on her chest, although her agreement with the entity had strict rules and she was unable to prevent it from killing Clara. (TV: Face the Raven)

Where is Ashildr when she becomes naked and how does it happen?