"She is a celebrity in China."
You wouldn't really need it as a Chinese sentence, but you do in this case for the exact translation. Without it as the article, you'd be saying "in China, she's celebrity"
True, but what confuses me is that you can say 她是医生 without using 一个, but not in this case when she is a celebrity?
In these simple sentences, 一个, 个 or nothing make no difference. In more complicated context, there may be a subtle difference in the meaning. But if you are still at beginners level you can safely regard them as interchangeable.
Today I come across a related question. Read this thread and see if it helps.
The goal isn’t a word-for-word translation, but to produce the most natural sounding Chinese sentence possible while conveying the same information as the English sentence
It's not about time in this sentence thought. Can place be used before subject too?
I think you've made that a topic-comment sentence now, which means you've switched the focus of the sentence from 她 (who she is) to 在中国 (happenings in China). Can someone else confirm?
Location usually comes first in a sentence. I don't know if it's technically "wrong" to have it somewhere else, but it just usually isn't said that way.
When referring to people, the measure word "位 (wei)" would be more polite/better, so 一位明星
Was it wrong to write “在中国，她是一个月星”？I thought I could place the time at the beginning?
The adjective for "famous" (or one of them, anyway) is 有名. You can look at that literally as "having a name." You might think of that kind of like "this person has made a name for herself." 有名 can also be used to describe famous places.
I wrote, "她是一个中国明星". It was wrong. I can see how the right answer is better than what I wrote. But I would like to know if anyone is willing to tell me why this construction is wrong. :)
Is it has to be place(adverb) first after subject? 她 是 一 个 明 星 在 中 国 .. is my answer wrong?
Adverb complements a verb or an adjective. So we consider its position relative to these components too rather than the subject. And yes it must be placed before 是 (the verb) when we want to complement 是 (so A is B in China but A may be something else if not in China).