She was never going to do that whilst the target of the campaign is Corbyn; people - especially Labour voters - like him, thats why he won their leadership election twice by miles and why when people actually see him (rather than viewing edited highlights of him from the media) his ratings go up. He is after all a bloke who lives in a normal house, who works on his allotment and who didn't cane the expenses when everyone else was.
The people she should have gone after are the Labour opposition, who are at least as (probably more) responsible for the party being divided, who are the reason why so much of the core Labour vote was disaffected, and who actually have a record to attack. She'd then be able to point out that, despite what is in the Labour manifesto, Corbyn wouldn't be likely to get much of it through because he probably wouldn't have the backbench support required and that he might not be able to form a government anyway. You also can't imagine that there would be that much solidarity from the Labour leadership if the likes of Woodcock, Gapes, and Blair were getting a shoeing every day on the campaign trail - Corbyn would almost certainly look to distance himself from them, which would make the disunity even more obvious.
Of course, what she has done is focused on Corbyn, the opposition have gone on strike (hoping to make Corbyn "own" the defeat) - so now Labour doesn't appear as disunited as it is and Corbyn and his supporters get their message out on live TV every day. It is a policy that is as successful as German battleship-building was at keeping Great Britain out of the First World War.