Hours after giving an emotional speech to the United Nations, Mr Trump appeared to troll the 16-year-old on Twitter.
He retweeted a video of her speech and wrote: "She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!"
Her account previously said: "16 year old climate activist with Asperger". It now reads: "A very happy young girl looking forward to a bright and wonderful future."
The teenager made an impassioned speech at the climate action summit and told delegates they would never be forgiven if they failed to tackle rising temperatures.
The teenager, who travelled to the US by yacht to avoid flying, said she should not be up on stage, but should be in school on the other side of the ocean.
"People are suffering, people are dying, entire ecosystems are collapsing, we are in the beginning of a mass extinction and all you can talk about is money and the fairytale of endless economic growth. How dare you?
"How dare you continue to look away, and come here saying that you are doing enough, when the politics and solutions needed are still nowhere in sight."