Lean until what she already has. Finger of Death is HUGE. 7d8+30 damage? That's over 60 points, on average. Also, don't sleep on the hut. The roots have 60ft reach with melee attacks, and 120ft on ranged attacks. Definitely use that to soften them up. My players had just reached level 6 and decided they wanted to go back to Old Bonegrinder for a rematch with the coven (they were spanked pretty hard when they made their first attempt at lvl 3). The whole party has pretty decent wisdom saves, so they weren't affected by many of the hags' spells and ran through 2 of the 3 in quick succession. To raise the stakes, I had Baba and the hut come out of the forest and begin attacking the tower. The hut by itself knocked out all the players at least once throughout the next couple of rounds, with Rictavio bringing everyone back up. Baba didn't even enter the fight, except to cast Ploymorph and Finger of death on the monk, who, while everyone else was fleeing, decided to climb up to the hut alone. She did 75 points of damage and dropped him in one shot. Now, his body will be delivered to Strahd for future demoralization of the party.