Sophia knew that there was no point in trying to hide her presence. The enemy may be incredibly weak right now due to the deadly wounds he received during his last fight but his consciousness was still on a different level since it had obtained a qualitative improvement the moment he had awoken his True Soul.
Above the egg, two eyes made of black fire were formed and the lava around them started to form shields and giant weapons that targeted the Neo-Demon. He had detected the woman the moment she entered the magmatic chamber, but moving from this location would severely harm his healing process so he was forced to wait until Sophia reached this area.
If his soul was in its peak condition, then he would not have needed to move to defeat the woman. He could have taken control over the entire magmatic chamber and used it to crush Sophia, but right now taking control of the lava around him was the best he could do.