In #2, using "until," she will be ready to leave by Friday, but no sooner. In #2, using "by," she won't be ready to leave on Friday - presumably when someone wanted to go. In fact, we don't know when she will be ready to go, but Friday is too soon.
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Marius Hancusome might find this useful:Thank you, Marius.
http://www.longman.com/ae/azar/grammar_ex/message_board/archive/
select/click on "until"
click on "By vs. until"
Anonymous
So, is it correct to say "He will beback inout of the office until Monday"? or "He will not be back in the office until Monday"? Okay