Little Demon Queen, the one you can fight during the exposition. The narrative explains that, just like post-GS Wu Heir and Tang Ruo(As Middle Houtians), she could fight against and defeat fairly strong Late-Houtians as a MH.
Just like Long Chen, LDQ has a mantra(A art from a Immortal Emperor) inherited from TW, that's, a forbidden Art that even Wu Heir would be able to use. Also has the Yin-Yang Heavenly Physique that's allows her assimilate others blood to increase her own Blood Purity when using the Purity Draining Needle(So she might be on the 90% range at that point), and as said in the Book, this physique paired with a good alchemist would allow her a extremely quick growth and potential to surpass the current Demon Queen. And the fact that LDQ is completely shameless and ruthless, highly Proficient in formations and probably Alchemy itself.
So yes, I see LDQ as a heavy-hitter, either she's the second or a separate contestant. My idea about this is that she's a LB disciple, one of the most prized/important, if the the most important and talented Disciple(Given Shengjue stated that He Gang was in the bottom list within the LB's disciples...).