I did this. As soon as I had teeth I bit my nails.
I was an anxious child and I become a anxious adult. I come from a long line of anxious people.
Biting was a habit that helped me cope with a world that scared me.
Please don't nag her to stop, as SURELY if she could stop she would. As I grew up I was acutely aware of my nails and how ugly they looked.
So what would have helped? 4 is a bit young to have talking therapy. However, I think I possibly suffered from a mineral deficiency as well as anxiety. I think I should have had anti anxiety meds early on, but no one will give children relaxants willingly. I am sure you would find the idea appalling.
I have actually stopped now as I have had acrylic nails applied ,and kept them on for six years. To be honest I think covering her nails is the only thing that will help her to stop. But at four she will pick them off, and she needs the comfort that biting brings.
Some of my cousins bit their nails as well, but stopped around 15. Apparently Most children bite or pick their nails, but stop around 14/15.
It has been re classified as self harm. Google the subject.
Are you and your DH happy go lucky relaxed sort of people? If the answer is ' No 'then I think you are going to have to relax about your DDs nail biting ( she is as she is) until she can take steps herself, to give it up.
The first thing I notice about anyone are their nails ( Princess Diana bit her nails, look at her engagement photos.) I am a pensioner and I see people my age biting, horribly
Sorry, that I can't be more helpful, but I tried everything to stop. Nagging me, just made me more anxious and made me want to bite.
If you took her to a GP about it I am not sure they could do anything. They could look for a mineral deficiency, possibly.
There have threads about nail biting on MNet before and nothing successful was ever suggested. So sorry,as it is so awful to watch.
Perhaps some child Psychologist can come up with something.