The Vacancy Act provides Sessions to be in his position for 210 days before Senate’s approval.
https://en.m.wikipedia.org/wiki/Federal_Vacancies_Reform_Act_of_1998
No, it actually says you can’t be acting if you were submitted for confirmation.
I think, ,reading the law, what they might be able to do is fire her, and then put someone else in — if I were trump, I’d see if there was a retired AG from a prior republican administration who would come back. Or maybe see if Rudy would serve for a while.