help with aggression towards a second puppy

Question
I am in desperate need of help... as I write this, my 8 week old Scottie is on
my desk because I am afraid to put her down.
I have an almost 10 month old West Highland Terrier (female) and I adore her,
she is highly intelligent.  I wanted to get her a playmate, so I thought I should
get a dog that will be same size, temperament, etc., so I got a Scottish
Terrier.  85% of the time, things go pretty well... they sniff each other and roll
around and play, and it appears to me that it is play (tails up and wagging
side to side, not straight up or rattlesnake-y wagging) but the Westie has
made 3 attempts in the past 24 hours at attacking the Scottie... she hasn't
drawn blood or done any physical harm, but its a full on growling and the
Scottie cries, so clearly its traumatic on both of them.  I keep the Scottie
crated while I am gone to protect her, they have seperate beds, and I have
been working on dominance with the Westie (no more sleeping on the bed or
human food treats)  I suppose it's also important to say that my Westie has
been around all sizes of dogs since she was a pup (though none smaller than
her I think) and has never shown aggression towards another dog or cat.
I am just terrified that one of my dogs will end up hurt or not being happy
pups, I love them both dearly and I will do anything it takes.  I know that the
socialization process with two dogs will take time, but I am just petrified that
they will not get along in the future.
I appreciate any help you can give me.

Answer
Sibling dogs do squabble but they rarely hurt each other. Sometimes when one is older than the other the younger one can get scared and freak out for no good reason and the older one may need to get a little grumpy to make sure the younger one knows who is boss. Oftentimes younger pups don't have good doggie manners and older dogs need to correct them. And there's always the sibling rivalry thing. Usually they work it out for themselves.

Focus your pack leadership exercise around resources such as food and toys so that these don't become objects to fight over. http://www.thegooddogjournal.com/2009/02/whos-boss-establishing-pack-leadership.... has some good information about establishing yourself as pack leader. Remember though that just because you are pack leader doesn't mean that they won't still need to work out the heirarchy among themselves, especially since they are both female. Make sure they are both neutered to minimize the effect of this. I think they'll probably get along fine in the future. Just break up fights when they happen and don't leave them alone together until they both mellow out a bit. They'll sort it out.


You asked about neutering:
Well, there are behavior issues. Dogs of the same gender tend to be more competitive with each other. But because they are female if you don't neuter them you and they will have to deal with heat cycles and those are just a pain. Plus, neutering them reduces the risk of many health issues dogs can suffer. You should talk to your vet about the pros and cons of neutering.