Do yourself a favor once you get the shadow groups cleared delay everything except finishing Lily's room and get your health up to around 300-450 as well as attack (attack maxes at level 5), your gonna need it for the next battle.
I made it through the attack on the cottage with under 200 Health.
I only have 240 now (level 29) and have never once run into trouble.
Pretty sure that Theo said, a while back, that he does test runs with minimal possible Health (i.e. no real farming for stats) to ensure that the battles are still able to be completed.
Think it was done by %, so whatever health you have, you'll be reduced to X % if you get the attacks right.
i.e. The more health you have, the higher the damage that you receive & vice versa.
Should need full Stamina, more than Health.