Oh, dear sweet angel of an anon. I’m sorry, but I don’t think I can fill this prompt. It’s an interesting idea to be sure, but I have a bit of… conflict of interest, I guess you could say.
I already have a series for an SI!OC also in the Sannin/Sakumo generation. It’s called (In)Difference and it’s about Kiyoshi Utsugi–the kunoichi on the same team as Dan Katou (aka, Tsunade’s beau) and Kunugi Mokume (some random ninja who had a full name, is approximately the right age, and was possibly crying when Dan died). And… she’s kind of Kakashi’s mother.
I haven’t written much for it, and not even very recently either, but I wouldn’t feel comfortable in diverting my era-specific attentions away from that series. I mean, arguably, since Sakumo’s kunoichi teammate isn’t my character, she very well could have been a Shikako reborn. But that kind of takes away from my story. And I sort of also have plans for Sakumo’s genin teammates. Unfortunate plans.
So… thanks for the prompt, anon, but I don’t think I’ll be filling this one. I’d be more than happy to help you brainstorm the idea if you want to take a stab at it yourself–similar to the back and forth collaboration I have with @kuipernebula for Team Medic–but I’m afraid I can’t commit to anything more than that.