They'll find the area where the slug originated, but there won't be anything of note there. However, if Ciri is sensitive to magic, then she will feel a similar magical energy to what the Summoned have felt around the ward in the Vaults.

The floor is mostly non-porous. It's made of stone, but there would be a bit of debris. Because the area was off-limits, there isn't too much dirt being tracked in.

If Ciri turns around, she will notice that a heart <3 has been drawn into what remains of the blood on the ground. It seems something wants to wish her and Aloy luck being gal pals!