I've never seen anything like that. Maybe someone else will come along and share their input.
Basing off how you said "you think" she is around four months, I'm going to guess you bought her just recently from a breeder, or hatchery?
It is possible there was some sort of environmental problem in the breeder's setup that may have caused such a problem to occur. For example too small of feeder openings, possibly wire in the pen and the chicken repeatedly kept pushing her head through thus rubbing off some of the keratin on the beak over time, or it could be caused by prolonged use of what they call " anti-chicken pecking glasses".
So as far as the cause, I would be inclined to think it may have been environmentally related, but there is no way to be sure unless you go back to wherever you bought her, and take a good look at their setup.
As far as what to do, if she's acting fine, I wouldn't mess with it. It may or may not heal over time.