This lascivious rocker is one of the last tunes written by lead singer Bon Scott, who died six months after the album was released. It's a classic Bon Scott lyric, as he finds myriad ways of explaining how his woman satisfies him, all while keeping the title squeaky clean and radio-friendly. It was released as a single in the UK and other parts of Europe, but didn't chart. In America, the song did very well on stations with the Album Oriented Rock (AOR) format.
Highway To Hell was the first AC/DC album produced by Mutt Lange, who employed various production techniques that made the band's sound more appealing to the masses without softening their sound. On this song, you can especially hear Lange's influence in the backing answer vocals ("girls got rhythm... back seat rhythm").
Lange was an up-and-coming producer at the time, but he would soon become a superstar, launching into the stratosphere with AC/DC's next album, Back In Black.
Note that there is no apostrophe in the title, which implies multiple girls having rhythm. The lyric suggests that an apostrophe is necessary, as Scott is singing about one specific girl, but it's not likely that anyone challenged his grammar.