In the movie, the beginning of Elvis and Priscilla's relationship seems smooth sailing and innocent. Priscilla's exact age isn't disclosed, and though it is mentioned she is "teenage," her portrayal by 24-year-old DeJonge ensures she doesn't look too noticeably underage when they meet. They get married and have a loving relationship until Elvis's decline pushes her to leave him. After their divorce, Priscilla confronts Elvis to encourage him to go to rehab.
In reality, Elvis and Priscilla met while he was serving in the military in Germany when he was 24 and she was just 14. He quickly began pursuing her romantically. Though Priscilla's parents initially didn't allow her to see Elvis after she came home late from a party, he eventually convinced them to let him court her. They had a long-distance relationship for two years once he left Germany, and when she eventually visited him in Los Angeles, he introduced her to drugs.
Priscilla was allowed to move in with Elvis in 1963 under the conditions that she attend a Catholic girls' high school and that Elvis eventually marry her. Elvis proposed in 1966 (and some claim this followed threats that if he didn't, Priscilla's stepfather would have him charged with sexual crimes against a minor). Elvis and Priscilla were also apparently not involved after their divorce, which makes the scene where Priscilla confronts Elvis about rehab is entirely false.