Thanks for the info, Brad, I'll see what I can find.
I don't know if you know the history of Nice. I knew some but when I started searching for my relatives. When I started having problems I read up on it. After that I had to approach doing research there in a whole new way. This should also give you an idea of why you're having problems.
First, when someone said they were from Nice (Nizza) they could mean the town or the province. You can see the problems that poses right off - lol.
Then there's it's crazy history. The province changed hands, size and language many times starting with the Roman Empire - I won't go into them all. In 1713 it belonged to Savoy. From 1744 to 1748 it belonged to the French and Spanish. In 1775 it was part of Sardinia. In 1792 the First French Republic had it (and used the crazy Napoleonic calendar so dates can be a challenge). In 1814 it was back to being part of Sardinia-Piedmont. In 1860 it was once and for all ceded to France.
As for it's geography - some parts of Italy used to be part of the province, so did Monaco and San Remo. The language was Latin for a very long time, then Italian, then French, back to Italian, and so on and finally just French. The names of towns would change with the language: Nice/Nizza, Castillon/Castiglione, and so on. Sometimes they refer to places by ancient and/or Latin names that bear no resemblance to any modern name, so cannot be found. Peoples' names changed: Giovanni/Jean, Joannes-Baptista/Jean-Baptiste, and so on.
Finally there are just the changes to the town of Nice itself. For instance, Saint-Dominique, the parish your great-great-grandmother was from, no longer exists and a few tiny villages that used to be separate are now part of the city.
I've gotten pretty good at the ins and outs of searching the province so I hope I can help. One thing for sure, the French kept great records so they're out there somewhere.