The lump appear 45 hours after delivery suddenly,she is feeding well,not pale and had no neurogical symptoms and the swelling was disappeared completely her position was changed

The quesition needs a neonatologist answer

Ask your doctor!

Why you would go on line to ask this question is beyond me.

Your doctor is there to serve you ,you are paying them .
If you don't understand what they tell you ,you ask them until they make it clear.

THAT IS YOUR RIGHT!