"She is walking on the beach in autumn."
Translation:Sonbaharda kumsalda yürüyor.
Lizmichel, 0, personal pronoun, subject, comes first in a sentence and is optional, when no risk of confusion. Excepted when you want emphasize who is walking. I think you can write: "Sonbaharda kumzalda O yürüyor" See "word order in Turkish" on Duolingo Turkish Grammar Portal and so many other sites.