No. Mia is not accused of a abusing a child, Allen is.
Mia didn't initiate the documentary, the victim of Allen's abuse did, Dylan farrow.
Regardless of how Mia dealt with the situation in 1992 (she shockingly finished making a film with Allen in the middle of the situation!) the alleged sexual abuse by Allen on his 7 year old adoptive daughter Dylan (now an adult in her mid 30's) is very credible.
The social workers in new York confirmed that they believed the child. One was sacked by New York under pressure from the state .. Allen is very powerful and popular in new York. The social worker was reinstated and his report, available to the public, includes a thorough investigation and includes all the elements that you would expect in an investigation into child sex abuse.