1) She probably hired someone for the task!
2) She thought she will never get caught as she was out of country
3) She killed her as she ditched Sahil/her sons ( thats makes her perfect wife/mom)
4) Remember she tells Lakshya on the phone she will fix everything when she comes back from wherever she was!
5) She is technically still Virani!
6) Ganga is like Tulsi - adarash indian bahu who will do ANYTHING to save her family so why not murder this bitch!
I think she will finally admit to her sin when someone else will get arrested and hence get all audience sympathy by owning up to save another " ghar wala"! This will be a good suspense too!!!! Rest all is too obvious!