In short, she/they is the most common way for a person to indicate that they go by she/her or they/them pronouns, likely with a preference for the former. 宾格 (him) 所有格 (his) 为什么还有这种现象？ 难道英国的女性地. In your example, she is being emphasised.
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According to grammar rules, it should be this is she, because is is a linking verb (a verb that connects the subject to more information about the subject), so it can't have an object (her), but it's.
The difference is that she's and similar shortened forms are used in colloquial speech, but not in certain cases.
译成中文的话 her 和 she 都是她。 但这两个字的用法不一样。举个例子，你自己感受一下。 she killed someone last night 她昨晚杀了人。 someone killer her last night. Taken from the free online dictionary:
