False accusations can ruin lives, which is part of the reason why our legal system requires substantial investigation and an “innocent until proven guilty” standard for criminal cases. Outside of the criminal system, in the US, there are legal safeguards like libel and defamation laws that give someone who is unfairly maligned recourse in civil court. And in the US and most other jurisdictions, truth is a defence against defamation – so if her father were to sue her for allegedly defaming him, he would have to show that her accusations are false.
Proof in libel runs the other way. She would have to show that her allegations are correct.