It's probably the case of Sakura taking her training seriously like how Tsunade took her seriously. Plus, we actually have a statement from the Boruto Movie where it said that Sakura passed down her strong fist technique down to Sarada. And we didn't see Sarada training for it in the Boruto Movie, nor the Gaiden.
So the best possible conclusion is that Sakura is training her, but not as her mother, but as her teacher. In regards to what-ever Vulpini said above, Kakashi isn't connected to the Academy, so based on that logic he wouldn't be her sensei either. Boruto just assumed that honor students had it tough because she was training late.
Back to what I said about Kakashi.
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He left for his trip around the time Boruto was lashing at due to his father becoming Hokage.
In the Naruto Gaiden, which takes place years after Chapter 700 (according to Kishimoto Sarada is 11 in the Naruto Gaiden, and in the Naruto Anime/Chapter 700, they are probably around 7-9 years of age).
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Meaning Kakashi is on his trip with Gai still a few years after 700, and, he isn't present in the Boruto Movie. I can assure you that he isn't training one. It's going to be Sakura.
Unless you think it's Shino, which could be possible since she's their sensei. Or it could be Konohamaru! But I'm going with Sakura due to Sarada going to learn her Shannaro skills in the next upcoming arc: Gaiden, where she shows off her monstrous strength inherited from momma.
Believe what you want though. Just speaking IMO
I explained it above you.
