Why do we have 好 in translation of "You're beautiful"?
It's rare to use "noun + adj" as a whole sentence in daily life. Usually, people will add "adv" before adj to make the sentence sound more comfortable and normal.
For example, in your example, people usually say:

你好漂亮

你真漂亮

"好" and "真" means "very" here, but the speaker doesn't intentionally want to express this meaning. These words are used here just because this is a common structure "noun + adv + adj" to say in daily life.

Another example:

今天天气真好 What a good weather today
Without 真, it becomes 今天天气好, which sounds strange because of its core structure "noun + adj" as a whole sentence.