The quest for the black dragon

When you were younger, out on a rainy day walk in the woods, you rescued a dying, lone young dragon, whim you saved. Her name is lilith, but you call her lily. Now, having matured significantly, you set off on an adventure, as a warlock, and her as your familiar. What you are yet to find is, she is the last living obsidian dragon, who can control all elements (ice, fire, water, acid, all typical dragonborn types). You are on a quest to rid the world of demons who rendered her in her prior, weakened state.