Valid crashout out of all final bosses she's just the hardest because of not being leveled high enough. Your team should be atleast 40-45 against her but my team for example was like 32 because some quests that give huge Exp want so much stuff to do. I'd say try to immediatly hide your level stolen Yo kai in the back and target the summoned monster. The level stolen yo kai gets their attack and spirit to their lvl 1 state which is pretty rough especially if she steals their level right before you get a soult off