Hmm.

My opinion on this matter, it is better if you will focus on the ninja that you will use more and much more useful these days. And if you don't have enough coupons to complete your plans then you better postpone it and save up first to get a better deal. Thank you.

Congrats! And I wish you good luck for her breakthroughs :p

Hmm.

It will differ from each player based on their prospectives but the majority and for me, the very important ones are the Passives. The scaling passives would give her the most advantage in every battle whereas she gains more Ninjutsu for painful damage or the Resistance scaling where she gains a thick anti-damage from opponents, and of course her self-healing passive to sustain her for her to last long in battles. The next skill that you should target would be, either the Mystery (where she gains additional percentage damage which is kind of related to her Ninjutsu scaling for maximum output damage) or her Chase that gives her the ability to chase twice, and that means additional chance to reset her skill and lastly, her standard (but you have the option whether to choose the Chase or the Standard first, depending on your choice).

That's what I did to my Kushina [Red Hot-Blooded Habanero]. For you, it is still up to your choice and your preference. Good luck and have fun wrecking your opponents :p . Thank you.