Giving Sivir a gold generation new passive or active.
Take this as a what if scenario. Because as far as i understand, given her VO, she's a pretty greedy mercenary.
And other champions with gold generation abilities like GP and TF have them because it´s part of their theme. GP plunders gold because he's a pirate. And TF gets RNG-based gold because he technically gambles ingame and always wins, regardless of the amount.
Sivir, however, despite having almost all of her voice lines be related, directly or indirectly to gold or building massive fortunes does not have a similar ability.