Gladiusx
That’s actually a good plan from Cersei. I think they didn’t do it in canon because the Faceless Men quoted a very high price to kill the Targaryens. It was something like millions of gold dragons. Tywin wasn’t willing to spend that much because with that money, he could hire an army for that price. It’s possible, if they were willing to spend that much money, the faceless men would and could have killed the Targs early on before she got her dragons. Very dumb that no one was willing to pay the price.