I wouldnt put too much hopes on them setting another spending event for Tsunade. Typically the recharge/spending event ninjas appear once, because another appearance means that the heavy spenders that already got said ninja during the first event are less inclined now to spend/recharge for duplicate frags.

They might release something along the lines of a "pick your..." like how the recent event was where you could choose between 1st till 4th hokage, but I highly doubt a "spend/recharge X for Tsunade frags" will come back. I could be wrong, but cant recall a similar occurance so far (cept maybe Minato and he isnt really that gamebreaking)