She was fired because she forgot to hand out the documents to the cabinet members before the meeting.
A big servant is bigger than the rest of the servants. One type of servant is one who serves the people (as is the case with this one). A big servant is someone high up in the realm of serving the people. So, let's call this big servant a minister or cabinet member. Big cheese.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.