The name itself isn’t too bad, even if it was completely made-up. However, I’ve read a couple of fanfiction stories where Nessie is named after Edward’s mother, Elizabeth, instead. One person, Xavier2163 being the Fanfiction pen name, even had the idea of having Renesmee be the middle name, so the name sticks around, but Nessie doesn’t get teased about it later on. I, for one, am not opposed to having the name changed to Elizabeth. The name change also leads to a less upsetting nickname, that being Lizzie. That way, newborn Bella is less likely to throttle Jacob for imprinting on Nessie, which wouldn’t happen in my version of events anyway, but that’s for another post. In short, changing Renesmee’s name to Elizabeth would be a good idea, as it benefits all parties involved, plus it’s a better name overall.