After any head injury
, if there was no Ear/ nose bleed, seizures, altered mentation, drainage
of clear fluid from nose etc- you need not worry.
Since the dent is persistent- there might be a simple fracture
of the skull bone.
Usually it takes about 3 months for such fracture to heal.
Since its already 1 month post the incident and no major problems were there, you need not worry.
You may wait. But if you are worried of cosmesis, then you may approach your Pediatrician/ Neurosurgeon who will be able to guide you accordingly.
Hope my answer helps you.
Wish your daughter good health.