Rescue girl with an unusual habit

[Aimz]

Hi all, we recently rescued a 4 y.o choc labradoodle named Lucy. She was used as a breeders dog, however her litters were not big enough so she ended up in a rescue home. She is just amazing, a bit shy, in need of love good nutrition but still keen to socialise and play.
Not sure if it is a nurturing thing from having her pups but when she is comfortable to come up for hugs, she starts to do what seems like grooming us. Not a big deal except she nips which can hurt the kids. any one know why this might be and what we can do to curb the only habit our beautiful girl has. Thanks alot.