She previously served as the Leader of the Welsh Liberal Democrats from December 2008 to May 2016 and subsequently from June 2017 to November 2017 in an acting capacity.

[3] She then returned to work for the learning resources department of Carmarthenshire College in Llanelli, before taking up a post as a marketing and public relations executive for a small business in Cardiff.

[6] On 8 December 2008, Williams became leader of the Welsh Liberal Democrats, having defeated Cardiff Central Assembly Member Jenny Randerson.

[12] In December 2012, Williams won ITV Wales' Assembly Member of the Year Award in a ceremony at Cardiff's City Hall.

In the Queen's Birthday Honours 2013, Williams was appointed Commander of The Most Excellent Order of the British Empire for public and political service.

[16] In the elections to the Welsh Assembly on 5 May 2016 Williams retained her Brecon and Radnorshire seat with an increased majority.

[19] On 27 October 2020 she announced that she would not be seeking re-election in the 2021 Senedd election, saying that she was "looking forward to spending more time with my family and I remain committed to my role in Brecon and Radnorshire and look forward to continuing to campaign with my successor to ensure Brecon and Radnorshire returns a Welsh Liberal Democrat voice.