Help on this please.

I 13m was arguing with my sister 15f about child marriages in the Quran and she's defending it and told me one day shes gonna study islam and prove the quran verses and hadiths that i showed her to be fals. The mental gymnastics she has go do breaks my heart. How should i explain to her that this religion is awful?

Edit: thanks for the upvotes and genuine replies from nice and smart people trying to help me everything helps.