Do you mean the original Latin feminine forms? Because that would be like asking for the English feminine form of Smith, Jones or Robinson. No such animal!
Nerina, to my knowledge, has the same meaning as Marina. A consignment of flower bulbs was being sent from South Africa to Europe in, I think, the 19th century when it was shipwrecked and some of its cargo was washed up on the Channel Islands. A particularly lovely lily got the name Nerina and for a long time was thought to be a native of Jersey; then it was rediscovered here and history got rewritten. So I don't see a direct link to Nero, unless his name had a Greek origin; which seems unlikely.
But there's nothing to stop you, or anyone, from inventing modern fem forms of these names if you'd like to.