In final selection, yumiko wore shinobus hoari. This was before she had sympathy for demons like tanjiro. So she killed the demons she found with no mercy. Until she found some demons that didn't attack her, she simply gave them a poisin that would kill them with no pain.
Basically at first she started using insect breathing to kill demons on the mountain. But she found a demon who was starving and didn't attack her. She felt bad and simply gave the demon a painless poison to kill it. Turns out it wasn't one of shinobus poisons, she made it herself. That kind of started violet breathing. During the rest of final selection, she either avoided demons to not hurt them, or she quickly and painlessly killed them.
Unless it was an evil demon, she simply sliced its head.
She tried her best and did save one other person at final selection, but the others died.
Later on the person she saved committed suicide
So in all, yumiko was the only survivor.Her outfit