Theidea soon reached to conviction, as she observed his increasing civilitiestoward herself, and heard his frequent attempt at a compliment on her wit andvivacity; and though more astonished than gratified herself by this effect ofher charms, it was not long before her mother gave her to understand that theprobability of their marriage was exceedingly agreeable to her.
请教老师：这里longbefore是副词词组，her mother之前是省略了that, 即thather mother gave her to...整个一句是形式主语it的真的主语吧？
你的剖析不对。It is not long before... 句式一般应如此理解：
it=主语
is=系动词
not long=表语（long 是时间副词，作表语）
before=时间状语
句意：在……之前，时间并不久。
例句：
It is not long before he comes back. 过不了多长时间他就会回来。
It was not long before he came back. 没过多长时间他就会回来了。
It was not long before he sensed the danger. 他不久就意识到了危险。
It was not long before I realised the enormity of my faux pas. 没过多长时间，我就意识到自己有多么失态。
It was not long before a helicopter arrived on the scene to rescue thesurvivors of the plane crash. 不久，一架直升飞机飞抵飞机失事现场，来搭救这几个幸存者。
