+Hp / - def or -atk are the best mood for her regardless your power. If you use her with azure fang in immortal lineups i suggest you the latter since sakura is not there to directly deliver damage but to spread poison so 1 stack of buff cover for the -5%, if you use her with cf i suggest the first, but you don't absolutely want she dies so you can not reduce defense and resistance. So why hp instead of ninjutsu? Because her selfheal is based on hp and both mystery and passive just get a 25% and a 18% benefit from more ninjutsu something that gets fully negated by a ton of debuffs while the self heal gets negated only by ignition, so, in many real life situations is better to be able to endure 2-3 more hits and to heal back more while chaosed or immobilized than healing maybe 300-400 hp back more only if your ninjas are not ignited.