Complex sentence: In 2003, Stewart switched networks once again, this time from ABC News to MSNBC where she was a daytime anchor and is the primary substitute host for "Countdown with Keith Olbermann", occasionally filled in as newsreader on NBC's "Weekend Today".
Split into simpler sentences: In 2003, Stewart switched networks once again, this time from ABC News to MSNBC where she was a daytime anchor and primary substitute host for "Countdown with Keith Olbermann". She occasionally filled in as newsreader on NBC's "Weekend Today".