"She feels hot in summer."
Translation:उसे गर्मी में गर्मी लगती है।
I am also unclear on this. Sometimes it is required before sometimes required after. It is hard to distinguish when an answer is not correct Hindi and when Duolingo is just being inflexible in its answers. It would be great if a new tip could be added that make this subject clear. I appreciate the contributors trying to help, but greater clarity from the course would really help.
As many have asked here, गर्मी में उसे गर्मी लगती है should be accepted as a correct answer. It is subtly different, and can be translated as "In the summer she feels hot". However given how loose most of their English translations are, they shouldn't be that nit picky. In fact in the same lesson they translate सर्दी में मुझे ठंड लगती है as "I feel cold in the winter".