额,我是学英语的.
She's back的意思是She is back.
并且,没有She has back这层意思.因为She has back这个句子本来就存在错误.
如果非要用has,那么句子就要变成She has been back.这么一来,缩写就变成She's been back,这样,根据语法就可以确定是is还是has啦.
楼主明白没?希望我说清楚了