How do I make Deste spawn in the Ancient ruins dungeon?

[Gorilla]

She isn't there after beating Anth, just an empty room

[Gorilla]

I've collected 99 monster shards as well

[Knight]

If it's empty, it means you already beat her. The game will add a warpwing to your inventory to send you home. You should sell the shards as it no longer has any use.

[Gorilla]

I found out the reason
To trigger the fight you need to talk to the underworld merchant at least once, without it he won't spawn in the basement

I'm doing a lvl 5 run and so never had a reason to go into the underworld