It's already a miracle that she slightly surpassed Tsunade, anything more is asking for the impossible
But seriously, considering Sakura's attitudes&skills i would say the most natural power ups for her that also don't ruin the feel of her character, would be:
- Genjutsu, both individual Genjutsus with high potency and large AoE ones.
She is a master at fine chakra control and had Genjutsu attitude from P1, although she never developed it and focused exclusively on medical.
So it seems a natural power up for her if she went and actually trained it;
- slug sage mode (Hashi Sage Mode).
Again fine chakra control skills and also fits perfectly with the strength&physicality fighting style she has.
Her strength would explode with this;
That's it.
These are the best and most narratively consistent power ups you can give her imo.
Maybe you could add some mid ranged acid Jutsu, poison hax, and similar.
But the "feel" of her character will start to get ruined by adding more and more stuff that is increasingly more distant from the strength, regen & medical tier chakra-control themes.
Wait wasn't Hashi's SM slug SM? Or at least that's what i always assumed
