Standard procedure with these events is having the final map (that actually drops her, technically final map is always the one that only drops spirits) be the highest drop rate at 50%. some people have been reporting absurdly good drop rates (one guy on the wiki had 8 drops in 8 runs!) so maybe it's higher this time but I doubt they'd make it special for this one, considering the translation screams "Nutaku will be taking over so we original devs don't give a damn anymore! Blame google translate!"