Could have been pinched by another hen or she got it hung in something.
I'd just monitor it for now if it's not bothering her. If it worsens and/or if she becomes lethargic/acting like she's not feeling well, then it's time to be concerned.
Welcome To BYC @Penny_01 :frow
Can you please post photos of your pullet and affected wattle?
Where are you located in the world?
Do you have snakes or insects that could have bitten her?
How long has this been going on?