As interim leader of the Labour Party, Harman's come in for a bit of stick lately for supporting (or at least not opposing) some of the Tory welfare reforms. But with the leadership election on at the moment I reckon this is a deliberate, calculated move.
The grassroots are a bit upset after taking a kicking at the election and seeing the unashamedly left-wing SNP doing so well in Scotland, bolstering their belief that if Labour went back to it's socialist roots rather than trying to emulate the Tories they would be electorally successful again (which plays into their comfort zone and tells them what they want to hear, which is something lefties *love*).
At a time when it's pretty irrelevant what Labour say on anything, Harman is using the opportunity to deliberately play the bogeyman so that the leadership candidates can publicly disagree with her and look 'tough' by telling the grassroots what they want to hear - giving weary supporters something to cheer about and rally behind when they might otherwise just dissipate and leave the party for being too 'Tory-lite'. For those at the top of the party it's not about making Labour electorally-viable again for 2020, but trying to shore up enough core support to stop the party becoming an irrelevance in the face of the SNP's lead as the most vocal and effective opposition to the Tories.