[JoeyP]

Oh this needs to be nipped in the bud (Pardon the expression) right away
Do not let your granddaughter near this pup unsupervised
You failed to mention how old your dog was
It sounds like it's no longer a pup which would make sense because it's probably because this dog had some bad expiriences before
Yorkies and kids don't make a good mix in general
Kids tend to act fast and make jerky type movements
and this tends to get Yorkies hyper because it sets off their hunting instincts
and kids tend to reach out and grab them
They're little guys and that can seem threatening
And lastly ... since your pup snapped at her when she was on your lap
the pup might be guarding you

what you do is place the pup on your lap have your granddaughter sit on the couch without making eye contact or petting the dog
have her drop treats every few mins
If the dog barks or growls .... OFF he goes... and onto the floor
keep repeating this again and again each time having your granddaughter get closer and closer