Apparently a lot of people have trouble with this boss, so here's me beating her at level 9.
The most generic characters with the most generic builds.
With a tiny bit of thinking.
I even get surprised at the beginning.
Game is available on Steam at store.steampow...
The English is currently auto translated so it's rough, especially if you don't fully understand all the mechanics and systems available, but it's pretty fun. The (solo) dev is currently taking bug reports and feedback, so feel free to give (constructive) criticism.
Don't be that guy who talks about nerfing a level 7 boss because he somehow can't beat her at level 12.
Addendum: One of the reasons I really like this game is that it encourages long dungeon crawls. As exploring time goes up, so does something called Mana Pollution, and with it a host of ill effects. However, like Darkest Dungeon, your drop quality goes up quite a bit with the amount of pollution, at max you'll be getting +3 to +5 modifier drops constantly. Furthermore, you can keep pollution by using the expensive heals at the temple rather than the inn. (There's the small issue of turning to ash if you die with high pollution that costs thousands of gold to revive but well, we take those risks.) There's also a straight drop rate buff for consecutive encounters (you can't carry that between dungeon visits). Combined with the camp system (I didn't use any camp buffs nor eat any inn food for this boss cause I forgot), you're just allowed and incentivized to just grind for long periods of time in the dungeons with risk, which I really like.