She's probably bored. But I agree with eeeefarm that you need to tell us much more about WHEN this destructiveness occurs and if she is alone when it happens, how long you leave her alone for and is she penned or free when she destroys things ?
Personally I would always take care that dogs never had access to electric cables, wires or anything which could damage THEM if they damaged it.
I have never tolerated destructive behaviour but am not sure how I went about actually training my packs. It was simply not acceptable. Period. Not done. If they did something like shredding a newspaper I would scream and cry and make a BIG fuss - so if ever they wanted to punish me, they'd shred papers. They knew that way they'd attract maximum attention. Another breeder I know over-reacted with screams and tears if the dogs threw cushions on the floor. So if they were feeling particularly evil - they threw cushions on the floor. Both methods have the effect of channeling destructive behaviour into a totally benign activity which the dogs rapidly get bored with.
This is another case of 'I'm bigger than they are and it's MY house' -