My cat keeps chewing on the kitten's umbilical cord even though she already cut it

So my cat (Gabby) had her first litter last night (around 12:00 am), and successfully gave birth to a beautiful brown tabby. She did everything right-- she bit the umbilical cord so that there was only a inch or so left, and licked the kitten clean, ate the placenta, and began nursing it right away. (We believe this is her only kitten, due to her young age and the fact that it is her first litter) After that, she peacefully rested as the kitten nursed. Hours later, around 7:00 am, she continued to nurse it and take care of it. Later that day-- I don't have an exact hour, but maybe noon-ish?-- When the umbilical cord was dry, she began nibbling on it, even though she already cut it, and it was about an inch or so long. I wasn't sure whether I should let her, or stop her, or why she was doing it. She stopped, but continued to do it later. None of the umbilical cord has seemed to fall off, but I was wondering if I should let her chew on it, and why she is doing so? If I shouldn't let her-- what is the best possible way to stop her without damaging the kitten's umbilical cord? 

-Thanks!

Looks like she chewed on it a bit, it's a bit shorter...

 Please help, I don't know if I should stop her from doing this or if she has a reason to :c

I have really never heard about this question.   she is apparently careful with this nibbling, so it looks more dangerous than it is.  (inexperienced mom can chew too much, opening up the baby).

So, I hope and think its nothing much with it, but  If you can stop her, try to do so.   Try and put softly your hand inbetween, or try and avert her focus...

weigh the kitten every day, on a electronical kitchen / mail scale, in grammes.   So you see the development.

Good luck!