Her final remark was the straw

Her final remark was the straw ^ and I decided to clear out right away!

Could anyone explain to me what this means. I really haven't got a clue.

More accurately it should be 'Her remark was the final straw'. This relates to the Biblical story of a camel being so heavily loaded that, when one more straw was added to its load the camel's back was broken.
In your example her final remark was sufficient to make the recipient of her remarks up and leave.

Are you sure that's story's biblical? If so, which book of the Bible?