[9] In May 2003 Williams scored an unfortunate own goal three minutes after coming on as a substitute in Charlton's 3–0 FA Women's Cup final defeat to Fulham.

[12] In the 2003–04 season, Williams returned to form and was an important part of the Charlton Athletic side who challenged for all three domestic trophies.

[13] She started Charlton's second successive FA Women's Cup final in May 2004, but suffered another 3–0 defeat as Julie Fleeting scored a hat-trick for Arsenal.

[20] Williams missed two penalties, one in normal time and one in the shoot-out, as Everton were edged out by Leeds in the FA Women's Cup semi-final at Haig Avenue.

[25] In November 2012, Williams and Natasha Dowie left Everton for local rivals Liverpool, who were hoping to build a squad capable of ending Arsenal's dominance of English women's football.

They finished seventh of eight teams as Williams missed three months of the season with a hamstring injury[28] and coach Matt Beard departed for American National Women's Soccer League (NWSL) club Boston Breakers.

[34] During the return fixture in February 2002, her first start, Williams scored the opening goal from a free kick in a 3–0 win at Fratton Park.

[40] England improved and Williams, captain in the absence of the injured Faye White, scored in a 3–2 quarter final win over hosts Finland.

[46] At the 2015 FIFA Women's World Cup in Canada, Williams scored a 38th-minute penalty kick against Colombia, as England won 2–1 in Montreal on 17 June.

In the semi-final in Edmonton on 2 July, Williams converted her second penalty of the tournament, in the 40th minute, to give England an equaliser against defending champions Japan.

Two days later, and back in Edmonton, Williams scored another penalty, on this occasion in extra time, to give England the winning goal in a 1–0 victory over Germany.

Her crucial goal gave England their first ever win over Germany and secured a bronze medal, the team's best ever finish at the FIFA Women's World Cup.

[47] Williams was not included in England's squad for the 2019 FIFA Women's World Cup, but manager Phil Neville said her international career was not over.

[51] She made her debut for Great Britain in a goalless draw against Sweden,[52] before featuring four times in the tournament, as the team were eliminated by Canada in the quarter-finals.

[55] Williams was appointed Member of the Order of the British Empire (MBE)[56] in the 2016 New Year Honours for services to women's football and charity.