The Hasbro toy for Jyn Erso labels her as "Sergeant Jyn Erso" and repeats this claim multiple times in the product description. For instance:
Join the defiant Sergeant Jyn Erso on a top-secret mission to steal the plans to the Galactic Empire’s most fearsome and deadliest construction, the superweapon known as the Death Star, and embark on an epic journey alongside the Rebel heroes, where Imperial officers are charged with protecting the Empire’s invention against the Rebels at any cost.
This surprised me greatly that Jyn held the rank of Sergeant. I had figured that she was someone like Han Solo, who in Episode IV was not a formal member of the Rebel Alliance and did not hold a rank (and despite that, he too was allowed to participate in top secret meetings due to his connections to important people).
When did Jyn Erso become a Sergeant?