Complex sentence: From 2001 she was a weather forecaster for ITV Weather, in 2005 was demoted to ITV London where she spent five years, until she resigned to pursue a full-time journalism career after freelance stints.
Split into simpler sentences: From 2001 she was a weather forecaster for ITV Weather before moving to ITV London in 2005. She spent five years there before resigning to pursue a full-time journalism career after freelance stints.