Ms McKenzie, a senior executive in the employment services industry and mother of three, was a founding member of the party established after Basil McCrea and John McCallister split from the Ulster Unionist Party.She made the annoucement as polling stations closed across Northern Ireland on Thursday night."I would like to confirm my resignation with immediate effect from the executive," she said in a statement to party colleagues."I will, of course, continue to support NI21 but I'm looking forward to spending time with my family after a long year of supporting the party."So sad that freshpolitics has been let down by old politicians. I have resigned from the Executive but still fully support NI21.Tina McKenzie on TwitterIt is understood that other senior NI21 members have also quit as the new party, which was contesting its first elections, spirals into crisis.It comes amid an intense row between party leader Mr McCrea and deputy leader Mr McCallister, which emerged after the party moved to clarify its decision to change its designation from 'unionist' to 'other' at Stormont earlier this week.Party officials said they wanted to clear up any confusion over the issue ahead of the European and local council elections.However Mr McCallister branded the decision "crazy" and said that it showed how "dysfunctional" the party had become.If elected I will stand but will not work for people who play dirty tricks and dirty politics.Tina McKenzie on TwitterOn Thursday night, Ms McKenzie said: "I wish John and Basil sincere good will and hope they can work out their differences for the sake of the party."She also stood as a local candidate in Belfast's Balmoral District Electoral Area and confirmed on Twitter that she will take her seat "if elected", before deleting her profile.Last month, she announced her decision to stand in the European contest, saying she wanted to promote a "united 21st century Northern Ireland".She added: "I want to maximise the potential of Europe and will focus on getting the best for Northern Ireland not the best for any one community."I want to represent and promote our people, their talents, skills, commitment and drive to improve Northern Ireland and Europe."