You were probably getting wrecked by conditions(burning or similar) from the random mobs in there.

If my girlfriend who is very bad at games managed to solo it, then everyone can.

Also, dodge isn't an ULTRA-SAVE button. You actually need to time it to be effective and that only comes with practice.

Another thing is that the red indicators on the floor are a bit wonky so please make sure you are entirely out of it and just on the edge of it. Leave a few steps between your character and the red indication to make sure it won't hit you.

Other than that, you need to clear the small mobs that are hitting you constantly before focusing on the boss.