In most common law jurisdictions, the executive branch doesn’t require even a victim, they merely need the elements of the criminal offence satisfied.

Not sure about the US, likely they need her to strengthen the case and won’t bother without her witness testimony.

I don’t think that’s right. In cases where the person pressing charges makes the difference between filing suit or not, it’s like because their testimony is crucial to the case. The government doesn’t need it, though.