"我姐姐做的甜点真漂亮。"

Translation: The dessert my older sister made is really pretty.

[Ryantheluckyone]

“The dessert my older sister made is very pretty” rejected 2020/7/19

[sovanyio]

"My older sister made a really beautiful dessert" rejected.
This translation is much more natural

[Keith_APP]

I think it is still fair to reject it because the subject in your sentence had been changed from the dessert to my older sister, while it is not impossible to retain the original sentence structure.