Get a lawyer because that's a Class A misdemeanor which has the potential to be on her record for forever. Any employer who does a background check on her will see it.
Evidence other than a breathalyzer(such as admission) can form the basis for criminal charges and conviction.
==================================================
Tenn. Code Ann. § 57-3-412
(3) (A) It is unlawful for any person under the age of twenty-one (21) years to have in such person's possession or to consume any intoxicating liquor or beer for any purpose, whether the same be possessed or consumed in a dry county or a wet county. It is unlawful for any person under twenty-one (21) years of age to transport any intoxicating liquor or beer for any purpose, whether the same be transported in a dry or wet county; provided, that this section shall not be construed as prohibiting any person eighteen (18) years of age or older from transporting, possessing, selling or dispensing intoxicating liquor or beer in the course of such person's employment. For purposes of this subdivision (a)(3), "beer" shall have the same meaning as provided in § 57-6-102.
(B) A violation of subdivision (a)(3)(A) is a Class A misdemeanor.
(C) Any person under twenty-one (21) years of age found to have violated the provisions of this subdivision (a)(3) shall, regardless of the final disposition of such violation, have the right to have the records, as defined in § 40-32-101, of such violation destroyed after the passage of six (6) months from the date of the violation. Such destruction shall occur upon motion of the person to the court which heard the violation and shall be without cost to such person. No violation of the provisions of this subdivision (a)(3) may at any time be used against the violator in any criminal proceeding.
==============================================