Before Shania, there was Olivia. In a greatest-hits concert Friday at the Chicago Theatre, Olivia Newton-John took the audience on a two-hour tour of songs that showed off her aptitude for country (“If You Love Me (Let Me Know)”), pop (“Xanadu”), rock (“You’re the One That I Want”) and ballads (“I Honestly Love You”). In the ’70s, when female country stars wore their hair big and their sequins even bigger, Newton-John – who was born in England, raised in Australia and pretty enough to be a model – ruffled many Nashville purists by winning the 1973 Grammy Award for best country vocalist.