2 of my 3 kids are nail biters. My husband is too. When he was young, he was tortured with devices and yucky tasting things to try and stop the habit. I wasn't going to do that to my kids.
I believe it's one of those things that the nail biter has to decide (like quitting smoking). No one can force you to quit. You have to WANT to, then get help.
When she is this young, and new at biting, try to keep her hands busy. In the car, watching TV, or any idle time, give her a toy or Cheerios or a book. Hopefully you can gently ease her out of it before it's stuck for life.
If not, teach her when it's inappropriate to have her hands in her mouth (just like if she were a finger sucker). When she's older, you can encourage her to have nice nails so you can polish them. She needs to want to quit.
My kids are old enough to understand that putting your hands in your mouth increases the chances of getting sick, but it doesn't matter. It continues, just like their Dad.