Just a quick notice!
So far, I haven't revealed the OC's name yet. What you know about her up to this point:
She has wavy, white hair cut into a medium bob, matched with green eyes. The two old ladies referred to her as young lady, but careful, she looks younger than she really is...
She is somehow tied to Momoshiki and Toneri Ōtsutsuki, but it is still unclear how and why. She is clearly not from earth! Yet she is acquainted with Itachi Uchiha.

Her known Dojutsus are the Rinnegan and Mangekyō Sharingan. Her known nature affinities: Fire. One trait of her Mangekyō is that she is able to consume chakra from her surroundings which then fuel her chakra reserves.
In chapter one, she used a sealing jutsu (Yasuda Clan: Realm of Death) which made sure that Momoshiki was never to escape from death. This bit of information might not really help you, but I assure you, it will all make sense later in the book!
Also, in the first chapter (where she fought against Sasuke) we learnt that she has the ability to fly, due to the white truth seeking orbits which she normally hides.

One more thing:
1 hour in space (f.e. in the Ōtsutsuki Realm) is equal to 10 months on earth. So time flies quite fast on earth.

Hopefully this is helpful!