Overall... I would agree with Ordieth117. Canon Nodoka as a protagonist would be hard to accept without changes to the character. To go from as she comes across in canon as vs. what you seem to want.
I can see such a change, but it normally would be a divergence early on and a big change to character.
For example, several come to mind with Genma dying and Nodoka out of some sense of honor taking Ranma on the training trip instead. She becomes a completely different person as a result.
RANMA 'A Little Motherly Love' by Celeste Byrd - [Status=Not Complete] - [Last Dld=03/17/2002] - [Size=199kb]
RANMA 'Chaotic Neutral' by Ozzallos-TeflonBooger - [Status=Single File] - [Last Dld=03/28/2008] - [Size=90kb]
Likewise, in others, she is obsessed with finding Ranma, leading her to do different things during those 10 years not in canon, she becomes a protagonist, but the stories are not generally centered on her. She does that in:
RANMA 'When you wish upon a sword' by Metroanime - [Status=Complete] - [Last Dld=12/11/2002] - [Size=164kb]
R-SM 'Princess of the Moon' by C Rose - [Status=Not Complete] - [Last Dld=01/21/2007] - [Size=1741kb]
R-SM 'The Return' by Josh Temple - [Status=Not Complete] - [Last Dld=10/18/2008] - [Size=2692kb]
A couple that might fit is her taking a broken Ranma under her wing to train him in the discrepancies caused by Genma. She does that in:
RANMA 'Out of Time' by Trimatter - [Status=Not Complete] - [Last Dld=12/25/2007] - [Size=432kb]
R-SM 'No Chance for Fate' by Tribun - [Status=Not Complete] - [Last Dld=01/22/2009] - [Size=200kb]
Another more supportive role might be as she is in:
RANMA 'Only You' by Tsunami-Saotome - [Status=Not Complete] - [Last Dld=11/05/2005] - [Size=307kb]
What is the story you are reading? So we can get a better feel of what exactly it is you are looking for.