While that's cool, is there a reason not to push chakra and shadow clones now? This seems like the ideal time, with a party member with enough xp, and a protegy teacher.
Honestly, I'm leery of trying to metagame Akane's XP expenditures. Until quite recently she has little idea she was going to become officially part of the Goketsu and thus gain access to the rights of top-tier secret techniques and the like. And without the expectation of eventual Shadow Clone I just don't buy Akane pushing Chakra Reserves over her primary combat skills or rounding out other parts of her build (her skill pyramid is pretty stretched, she could use a couple more 20's and 30's). Spending XP is retroactive wibbly casuality and technically we can spend it on anything but I don't want to poke the veil by having XP expenditures that don't make sense for the periods of time they represent.
Pushing ridiculously high Elemental Mastery is
slightly more plausible, since it's one of her most unique advantages and it's good to capitalize on it, and it's a pretty good area denial technique, but at the same time if Akane said that she spend the last few months exclusively training Elemental Mastery I'd squint at her because it would seem very odd for her to suddenly value this one jutsu over the entire rest of her build.
I personally think that we should divide her XP between rounding out her build a little, pushing her main stats, and then putting a little off to the side to maybe push things in a preferred direction a little. For example:
Elemental Mastery 10->20 (155 XP)
Chakra Reserves 17-22 (200 XP)
1009/1364 XP remaining
Getting Elemental Mastery and Chakra Reserves more build presence serves our meta goals but is also reasonably in-character. Akane would appreciate the value of good chakra reserves and stronger area denial, especially in moderation not consuming the entirety of her focus. From that, she could do something like this:
Alertness 30-40 (355 XP)
Physique 25-30 (140 XP)
Taijutsu 40-45 (215 XP)
Trapmaking 30-35 (165 XP)
Flame Aura 10-20 (77.5 XP after EM discount)
And that would leave 56.5 XP left for tweaking the numbers a little or putting a bit into bumping socials or getting a couple other skills to level 10 for the skill pyramid. Either way, something like this is something I'd easy buy her spending her time on.
(If you have a keen eye you'd probably notice that Akane wouldn't have enough 30's skills to support Alertness 40, but she could just leave it at 39 until she gets something else up to 30 or pushes Taijutsu up to 50.)
In conclusion, yes it's tempting to treat Akane's vast swaths of unspent XP as a blank check to level anything we want, but if we blatantly metagame her stats it'll
show in the story as an inexplicable choice for Akane to spend the last few months grinding CR way past where it needs to be to the exclusion of her primary and supplementary skills. Instead we should focus on the general shape of how Akane would spend her XP and tweak the edges to befit our intentions without making the choice odd.