I recently used this for a party of 6 level 6 characters. Yes, a TPK would have been easy. I had them encounter her away from the hut and skull and it was still brutal. Best to give your players an opportunity to run when they realise they have encountered something truly dangerous.
You definitely get your money worth. The stat block and new spells made combat dynamic and interesting for the DM and players. I had to pull punches to make the fight 'fair' and I will be bringing her back to stalk the players across the plains.