He said this is what led to her being appointed to a tough role as Minister for Health.
"Sinn Fein is seeking in this election a stronger mandate to enter forthcoming political negotiations come March to defend your interests and put firmly the peoples social, economic and political interests first".
Sinn Fein signalled a shift to a new, post-conflict generation in Northern Ireland on Monday when the Irish republican party named a 40-year-old woman to replace a former IRA commander as its leader in Belfast.
"It really just gives me vast pride to be able to say I'm going to lead our party in the future", O'Neill, a former Northern Ireland health minister, said.
O'Neill was 21 when she began her political career as an advisor at Northern Ireland's devolved assembly in 1998, the year the Good Friday peace agreement was signed, largely ending the bloody period of "The Troubles".
Mr McGuinness resigned as Northern Ireland's deputy first minister earlier this month over the handling of the controversial "cash for ash" scheme, which meant power-sharing ended and an election was called.
However referring to Martin McGuinness' statement that there could be no return to the status quo at Stormont, she added, "There is an opportunity for an absolute step change and fix something that is wrong".
Speaking upon her appointment, O'Neill said that it is a huge honour for her.
Ms O'Neill said being a republican was her "way of life" and assured Sinn Féin supporters: "I won't let you down".
In this role she successfully negotiated a new Common Agricultural Policy (CAP) programme securing the largest ever rural development programme to support farmers and those living in rural areas.
"I have never been afraid of challenge, and I have never been afraid to act", she said.