I basically put down the items that I did well with when trying to make her more aggressive.
I mainly build lich bane as a priority because that is all you need to be able to pull out decent damage, without effecting her supporting ability. You basically have your passive skill, stacked with the bonus damage from your Hymn of Valor, and on top of that is lich bane giving your about 200 bonus damage.
Basically its like this:
After her power chord is either at 2 charges or ready to go you do Hymn of Valor dropping down 250(+140ish) magic damage. Then you attack dealing about 130(+200) physical damage and about 780 bonus magic from power chord. a total of about 1500 damage, with their resistances subtracted of course and this is without using her ult to stun them first which deals 350(+160), which would put your output to about 2000 total damage.

Yes you can kill champions, or you can focus on bringing down their health and having your adc take em out.