Just seconds ago Variety.com announced that CBS' Supergirl has found their female villain, Livewire. Welcome Brit Morgan to the cast as Leslie Willis or Livewire! Morgan is known for her role on HBO's true blood. As for what we can expect from Livewire, according to DC Wiki:

She is a being of pure energy, able to transform into electricity and travel through anything that will conduct an electric current. She can externally manipulate electricity (along with electric and magnetic fields), and conjure lightning blasts of various intensities and lengths. In her electrical state, she can possess and control any devices along a grid that conduct electricity. Her lightning blasts can weaken or stun even Superman.