(Reuters) - Mary Bono resigned as interim chief of USA Gymnastics on Tuesday, only four days into the job, after she drew fire for a tweet she sent criticizing Nike Inc's NKE.N use of former NFL quarterback Colin Kaepernick in an ad campaign.

Bono’s Oct. 12 appointment was criticized by leading gymnasts such as Simone Biles who questioned whether the former Republican congresswoman was fit to lead the organization as it tries to recover from a sexual abuse scandal.

In a statement, USA Gymnastics said it had accepted Bono’s resignation, which was in “the best interest of the organization.”

In a letter posted on Twitter, Bono said she stepped down after “personal attacks” and defended her First Amendment right to tweet a photo of her marking over the Nike logo on her golf shoes at a benefit tournament for armed service families.

Olympic-gold medalist gymnast Biles spoke out against the photo, which Bono said was her own criticism of Nike advertisements featuring Kaepernick, who sparked a national controversy by kneeling during the national anthem.

“*mouth drop*,” wrote Nike-sponsored Biles on Twitter on Saturday. “don’t worry, it’s not like we needed a smarter usa gymnastics president or any sponsors or anything.”

Bono in her letter objected to the Kaepernick ads’ slogan “believing in something even if it means sacrificing everything.” In her view, she said, it was families who lost an armed services member who “literally sacrificed everything.”

USA Gymnastics said it would continue to look for a permanent leader as it tried “to transform the organization at all levels to ensure athlete safety.”

Three-time Olympic gold medalist Aly Raisman on Monday criticized Bono’s former role working for law firm Faegre Baker Daniels, which was hired by USA Gymnastics when sex abuse allegations were reported against former USA Gymnastics team doctor Larry Nassar.

Raisman said lawyers at Faegre Baker Daniels knew of Nassar’s abuse in 2015, but the doctor continued to abuse children for a further 13 months.

“Why hire someone associated with the firm that helped cover up our abuse,” Raisman wrote.

USA Gymnastics’ board of directors on Monday said Bono’s work at Faegre Baker Daniels was not related to any investigation.