While Luna's descent into madness did start with her transformation into Nightmare Moon, there was another fight happening in her mind, and she was losing. Luckily, she had her own guardian to help her.
My very first (self-published) book can be found on Amazon Kindle for 5 or 12 paperback! If you love dragons, give it a look! https://www.amazon.com/dp/B0CSM7QQ2M