making作动词enjoyed的宾语（enjoy doing）
bring用原形是因为这个短语所致：make sb do sth
buying是因为before这个介词,介词后面的动词要用ing形式.
是的the dress后面省略了that/which,因为that/which作宾语,所以可以省略.
she enjoyed herself making the assistant bring almost everything in the window
主语 谓语 宾语 宾补 宾语 宾补 宾语 定语
before finally buying the dress she had first asked for
时间状语 介词宾语 定语从句（she前省略了that/which）
主句使用过去式是因为发生在过去,与从句没有先后关系.
很高兴为你解答!
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