You will actually see your first flower through some stalagmite/stalactite bars in the Ruins as a child.
But you won't be able to break through until you get a spear as grownup Aloy.
Once you're on your quest for fire arrows and tripcaster, you can return to the ruins location.
Follow the map south to the green arch icon marked as Ruins.
You will find the hole you fell into as child Aloy.
Jump down the left side to go straight to your original dropdown point.
Retrace your steps from your child Aloy journey.
On your left after the first bat tunnel, you should see the stalactite/stalagmite barred room that now has a floating purple icon in it.
Use your spear to strike down the stone bars and go in to claim your flower.
(Note: there will be two more such barred rooms in the Ruins that hold goodies and an item for another sidequest.)