No, it's not just that she would like to be president, as she averred on video last week in a weak moment, or that she has decided late in life to go full Bolshevik policy-wise. It is to establish her in the public mind as a serious candidate so that when she is indicted a hue-and-cry will arise that the move is a purely political act of revenge by the wicked Trump.
Of course, she's not a serious candidate because too many people recognize her naked corruption, and she's carrying so much noisome baggage that her entourage looks like one of those garbage truck convoys hauling New York's trash to flyover country. Prosecutors don't even have to search very hard for evidence of her misdeeds. It's smeared all over the swamp-scape in the established facts about the Steele Dossier and its engineered journey through the highest levels of the FBI and Department of Justice, and the wild machinations that ensued when the cast of characters in those places scrambled to cover their asses following the debacle of Hillary's election loss.