Furness attended Usworth Comprehensive School and represented Durham at County level. By season 2002–03 she was already playing for Chester-le-Street Ladies, alongside several other youngsters and former England striker Aran Embleton.
In 2004 Furness moved to Gateshead College to study sports development and fitness. She began playing for the women's football academy at the college and Sunderland. Jill Scott was a team-mate in both sides.
In 2006 Furness moved to Northumbria University to study sports development with coaching, and swapped Sunderland for Newcastle United. However, she had by then suffered a serious knee injury, which required two operations and the removal of most of the cartilage. Doctors advised Furness to stop playing football but she nevertheless resumed playing for Newcastle United.
In December 2009, Furness scored one and made the other for Mel Reay, as Newcastle drew 2–2 at OOH Lincoln Ladies in the FA Women's Cup—only to miss her penalty in the shootout defeat.
Furness spent the 2010 summer season in Iceland with Grindavik, then rejoined Sunderland – making her second debut for the club in a 4–0 Premier League Cup win over Newcastle in October 2010. After helping Sunderland win the Premier League title, Furness joined FA WSL club Lincoln Ladies on loan. She made a quick debut in Lincoln's 1–0 home defeat to Chelsea in May, the last game before the WSL mid–season break. She returned to parent club Sunderland before the WSL re–started in July.
In January 2017 Furness left Sunderland for Reading Women shortly after the Lady Black Cats reverted to part-time status.
Chester-le-Street director of coaching Bill Godward alerted the Football Association to Furness' potential at an early stage. However, she was overlooked by England because she was not attached to a club with a centre of excellence or academy. Furness then accepted a call-up from Northern Ireland, and represented them in an U17 tournament in Spring 2004. Although born and raised in Tyne and Wear, Furness was eligible for Northern Ireland as her mother was born in Belfast.
After representing her adopted homeland at U17 and U19 level, Furness progressed to the senior international team. In November 2005 she scored against Slovakia, in Northern Ireland's first competitive home match for 20 years. Following a two-year absence from the national team caused by injury, Furness returned in time for the 2011 World Cup Qualifying campaign.
She contributed four goals, including a hat-trick against Croatia, as Northern Ireland ultimately finished third in their group behind France and Finland. In November 2011 Furness scored in Northern Ireland's shock 3–1 Euro 2013 qualifying win over former World and Olympic champions Norway.
Furness also represented Irish Universities at the World University Games, playing in the 2009 tournament in Belgrade. Two years later she was named in the Great Britain Universities squad for the event in Shenzhen.Scores and results list Northern Ireland's goal tally first.