The Texas Rangers and the St. Louis Cardinals are tied 1-1 in the seven-game series.
Lovato's sister Dallas tweeted during Game 1 that her younger sister should sing the national anthem during the Major League Baseball championship series.
Game 3 airs Saturday and all games are being broadcast on Fox.
Lovato, the former star of the Disney Channel's "Sonny With a Chance," released her third album "Unbroken" last month.
The Associated Press contributed to this report.