Aggresive snapping

Question
I am the proud owner of a 14 week old mixed-breed female.  Her mum was a terrier (she looked like a black West Highland) and we're not too sure about her dad!  Judging from her coat and tail, I would hazard a guess that there could be a touch of Labrador; she has a beautiful black, silky coat and a long tail.  I have had her with me for 7 weeks now and we are falling into a good routine.  House training is going well - there is obviously the odd mishap, but generally, I think we're getting there.  The problem arises when I go to put her collar on.  She snaps at me very aggressively and turns what should be a 30 second action into a long, drawn out battle of wills.  I have ended up with her pinned to the floor as I struggle to get the collar on and then attach the leash.  Once this is over, everything is fine.  She really enjoys going for walks and is extremely well-behaved on the lead.  A similar battle then begins when we get home.  Although I have distracted her with a small treat and managed to put both collar and lead on with the minimum of fuss, I don't want her thinking she can, a) get the better of me, or b)get rewarded for bad behaviour.  Her attack is quite a defiant one and with her lips (?) being raised into a snarl, it is giving me cause for concern.  My young nephew and niece visit often and I have trained her to 'no biting, just licks' with them - so she does seem to be aware of what she's doing.  It just seems to be me that she tries to bite.   I know she is teething - she has loads of toys to gnaw on - and I don't really mind the puppy chewy bites, on the assumption that it's temporary.    Have you any suggestions as to why she is doing this, and how to prevent it?

Answer
Thank you for adopting.

The key to most behavior problems is approaching things using the dog's natural instincts.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/  For more on being top dog:

''Elevation for small puppies:  Sit on the floor and gently put your hands around your pup's middle, below his front legs, and lift him up.  He is facing you.  Hold him for 15 seconds.  Repeat until he no longer struggles.  If he is past 10-12 weeks, lift his front feet off the ground, but don't pick him up.  

Cradling for small puppies:  Hold your puppy gently on his back, as you would cradle a small baby.  If he struggles, hold him firmly until he quiets for 10-15 seconds.  With larger pups, you can do this as your sit on the floor, with your pup between your legs.

Quiet lying down:  Place your pup on the floor on his side, with all 4 legs pointing away from you.  Use your hands on his neck/shoulder area and middle, to hold him in this position.  When he is quiet, praise him.  Lengthen the time that you keep him quietly in this position.  When he accepts this position well, handle his paws and muzzle, while keeping him quiet.''

The quotes mean this isn't my original work.  It is copied from my Puppy Raising Manual.  I have long used these or minor variations of them, and they are very effective.  You may want to give him a belly rub while he is on his back too.  Helps bonding.  There is a big difference between him rolling over and demanding a belly rub, and you choosing a time to roll him over and rub his belly.  The latter cements your place as pack leader.