She can still keep her navel piercing in.
Not safely, no. Get a proper barbell.
As you would without a navel piercing, just be sure the navel piercing is the last thing you clean before you exit the bath.
Your question "Can navel piercing migration be down to growth" makes no sense.
Wash the piercing take out the jewellery and leave it alone. It will heal over in a few months or a few weeks it depends on how old the piercing is.
If it hangs or dangles chances are good that it will retain a piercing. Placing the navel piercing off to the side will be problematic for aftercare and irritation during the healing process. If you haven't had a navel piercing before then stay with something that is simpler to care for and will give a result a navel piercing is supposed to give.
Navel piercing could cost anywhere between Rs 350 and 500 with navel jewelery done by experienced piercer.
If you want to wear a regular navel ring in your inverse piercing, turn the navel ring upside-down, so that the larger gem is in the navel, and the smaller gem is below.
it is a plastic piece you put in to retain your navel piercing
A navel piercing will cause scarring no matter what. Whether you got pregnant or not.
Navel
There is no direct evidence of historical navel piercing, although there is a great deal of historical evidence regarding the decoration of the navel, both for ritual and aesthetic purposes.