Those trying to change society for the better, still have to live in that society. She cannot be reasonably expected to live in a cave by candlelight and be expected to mount a serious campaign to reduce our reliance on fossil fuels.
She is vegan. She tries to avoid air travel, and she undertakes small, environmentally conscious tasks like planting trees when she can and driving in a Tesla.
She is taking plenty of steps to minimize her climate impact. If we all lived a lifestyle in which we offset and reduced our ecological where possible, the world would be a better, safer place.
In going after the messager rather than the message, and attacking Greta as a hypocrite, the climate change deniers are merely demonstrating the validity of her arguments. Instead of engaging with her message, they would rather attack her behaviour, appearance and mannerisms. This proves her argument of "listen to the scientists" is inscrutable and is a testament to the moral bankruptcy of the individuals who continue to deny the existence of climate change in the face of overwhelming scientific evidence.