itch.io

Try reloading the world until you get a slot (the path on which you move through) that gives you the blessing which gives +2 shield each time you use a shield move. Now kill minor enemies until you get protego maxima (once you have protego maxima (gives +8 shield) and a good damaging spell you could aim for protego diabolica (gives +15 shield and is legendary) which makes the boss easy af but it's not necessary). Now go fight until you get sectumsempra (does 10 damage) or any move that does atleast 8 damage. Now you can fight the boss but remember to use all your defense moves in your deck first and chip her health away. Do not be greedy and take your time. This is how I beat it in the new garbage pve update. Hope this helps. 

Ah also you only need the blessing if you are going to fight with protego maxima. If you have protego diabolica then you don't need the blessing because she does about 10 damage each round and protego diabolica already gives 15 shield. Also remember to use multi target moves until you kill the snowman beside her then use the high damage spells.