She sure did a totally poor job of that. But Cruz was, in effect, a fucking liar. It may well be that converting to natural gas has been a huge impact on the US CO2 emissions but that is deliberately avoiding the fact that gas is half as bad as coal.
Coal is terrible in so many ways that being half as bad as it is still disastrously bad. He thinks he's made some point. What he's actually shown is that the US has to get off gas too and fast.