Our 13 week old Male Black lab (named Dr. Watson) constantly bites his leash when we try to attach it to his collar. He will happily carry in his mouth - but this is counter productive to training him to walk on a leash. We have several acres so we have not had to use the leash since we got him at 8 weeks - and we have not taken him out in public as he still needs his last vaccinations. Is he just too young to start leash training?
I didn't start lead training seriously till a bit older. I would take her out on a pupia harness which had a back attachment so a bit harder for her to twist and grab the lead. If she did though I would just swap for a small soft toy or ball, or ask her for a behaviour such as a hand touch. Everything is so exciting at that age, especially the big wide world, so I never ask for too much.
My rescue dog bites her lead , and at two years old, its a hard habit to break , so as advised by @Beanwood , a back harness is the best way forward, it works for me .
Bella my 2 year old black lab would do the same until I started using a harness with both front and back attachment points , I found her wearing this and me using a double ended lead attached to both points did the trick and also gave me more control as she was a terror for pulling .
I wouldn't worry too much. They are just babies at this age and it's all just a game. They generally grow out of this.