Either way she won't be missed. In fact this blog has no idea what she did for the country in the first place. Nor why she was made a "lady".
She was considered a disaster waiting to happen at the FO and seems to have been notorious for attending meetings where she took no part but instead wrote copious notes on what everyone else said. The general assumption is that she is planning a pay-day by publishing some dirt-filled diaries.
She may have decided that since this government has less than a year to run it was time to leave and cash in. She may also be planning a defection to Labour and have an eye on a government job after the election next year. As an unelected peer she doesn't need to worry about how her constituents would take the betrayal and she would need some time to bed into a new party.
One thing is sure, she won't be quitting the Lords and will be seen there briefly but regularly collecting her £300 daily attendance allowance.