Assuming you use the water blitz team, i'de say either defense or life.

Defense since its her weak point and one of the most common counters is to blitz her before she can move with LM.

Life, for the same reasons as above. However i would recommend life more since it is in your best iterest to have the fastest move 1 possible. Therefore use the head gear with initiative charm on her. The charm will also boost life so it has synergy with this mood.

-5 to attack for sure. Her chase is only there to be pretty, you wont deal any significative taijustu damage with her.

forget about BP when using mood. If you decrease her weak stat and increase her strong stat (for her its resistance) the percentage of gain and loss would result in the highest BP. Plus in most ninjas, using mood to increase atk or ninjustu usually translated to higher BP.

However what you want it for her to endure long enough to build chakra and rush the opponent. MB, root with mifune will rip her appart if you lower her life, even if you increase her resistance.

My advice would be to forget about BP when using moods. Look at your lineup and how to defend against possible counters.