May
this is about the time a dog starts testing you authroity over who is going to be pack leader. Dogs think in a pack, so if you let her be on the same level as you ie letting her sleep on the lounge or bed with you, this grants her to challenge you authority. Dogs should never be allowed to be put on the same level as us because this is how they get snappy ie little spiolt dogs.
Also, border collies are incredibly intelligents and they’re great dogs, trust me i have one. Becuase of there intelligence they can pick up bad habits when they’re bored, try to amuse her with training club or puppy school and get her to meet new friends, plus toys which alloo for greater mental expereince such as kongs and puzzles etc keep her stimulated for longer. Border Collies are harder because they’ve a natural herding instinct which also means shes trying to round you or anything else she can get her paws on. Stimulating toys will help with this as well.
or you could just make her fat lol like our vet told us
Answer:
Good luck. That is her herding instinct. She probably gives signals (crouching, etc) that she's thinking about it, and that's the time to correct and re-direct her. FWIW, she isn't really biting - it's a nip they use to herd. That's not much comfort to tiny children or people who don't know her though…
Answer:
If she’s 3 months old she won't be snapping/biting she’ll just be nipping.
My border collie did this, just say a firm “no” when she goes to do it, she should grow out of it though - my dog did and she is the sweetest thing alive now!!
Good luck 
Answer:
do as every1 else says use a muzzle, if you’ve little kids keep her away and if for some reason she bites you while you take it off, punish her, flick her in the nose, rather hard (with the muzzle on) and send her outside, dogs love attention so dont give her any
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A muzzle is really the only answer.
Dogs that snap and bite other dogs are usually being territorial .
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Training. Is this dog behaving this way cause it's scared? playing? resource guarding?
www.fearfuldogs.com
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Chew toys or a muzzle if its really out of control
Answer:
muzzle