My pup is 8 and a half weeks now and came to lie with me 2 days ago. My boyfriend bred her but we don't live together. She has been fantastic and met my 3 big dogs and a few others absolutely brilliant. However on reuniting with her sibling she became very aggressive and started growling and adopted a very dominant posture, i had to take her away. Is she likely to be a very aggressive dog or is this normal when seperated from littermates for a while?

Please don't worry perfectly normal. :-D

Bitches are generally much more aggressive in a litter, from the minute they begin to mouthe to being up and running they begin play fighting and it can become extremely aggressive, it is important for bitches to sort rank and it really does start with testing games so early on in their lives, and also with some of the dogs, others will get along well, but there will always be dominant dogs and bitches in a litter, and by 8 weeks the rest of the litter know who they are.

She does not need to even be seperated from the litter, this is why breeders don't really like to keep a litter for longer than need be as some of the characters in it will instigate such rough play fighting games and act on their instintcs, whereas we want human to dog interactions as we breed domestic dogs, it is all noise and rough play and one pup generally needs to yelp for the 'fun' to stop. Or we breeders step in to divert.

Will she grow up to be aggressive, absolutely not. :-D Puppy play is nothing to do with human to dog interaction, and it does not mean that she will be dog aggressive at all incase you are worried about that too. :-)  This is normal play in a normal litter, it looks and sounds horrendous I know but to other pups and dogs it means nothing, she will calm down with her sibling over time, so you will be able to walk and play together in the future.

As for human interaction, we just have to teach our pups that we are not dogs and they can not play like that with us, do this with praise and reward and time outs if she tries to get bossy with you.

She'll learn fast and no doubt make a great adult dog. :-)

Oh thank god, i was getting so worried. Shes a very grown up little pup at nearly 9 weeks and very confident in many ways, but i was surprised at how she was asserting herself over the the pup who is a very quiet one given that she has been very polite with every other dog she has met.
Shes amazing really. She is house training so quickly (although doesn't like it when its cold, wet and blowing a gale outside!) and has been clean both nights in her crate from 10.30 through to 7am!

dont worry at all...
its all part of establishing a pack, she probably recognises that she was the leader, and needs to remind her littermate of this!

Females tend to be more dominant in a litter... the bitch that i kept still tries to be dominant over her mum (unsucessfully).. and it can sound and look a bit scary, but they need to sort themselves out (unless real damage is being done of course)

Dont worry she sounds like a great little girl =]