Faith Hill and Tim McGraw when their youngest daughter, Audrey, reached a major milestone over the weekend and they were forced to say a bittersweet goodbye. The proud mom-of-three paid tribute to Audrey as she rang in her 20th birthday and bid farewell to her teens. MORE: Faith Hill and Tim McGraw get steamy in first look at Yellowstone spinoff 1883In a sweet Instagram post, Faith shared a throwback video of her lastborn showing off her singing talents as a young girl and belting out a tune by