3 year old & new puppy

Question
We have had a wonderful Toy Fox Terrier for three years now. She was about 9 weeks when we got her. Sophie is very smart & very loving. We got a male TFT about 4 weeks ago (at 7 weeks)from the same breeder, and they are true brother & sister. His name is Max and seems well adjusted, full of energy, and very curious. Sophie has pretty much ignored Max from the start. She would growl a bit or just move away. Max wants to play and will chase after Sophie if they are near each other. We assumed they would get along eventually, but recent behavior has us concerned. Sophie no longer growls at Max and seems to have become terrified of Max. She runs away or jumps up on a chair or into our arms, shaking. She would stay upstairs away from Max and all of us rather than getting near Max. Do we keep them separated until Max mellows out, do we force the issue by making them deal with other? We love them both and want them to at least get along.

Answer
If your dog was not well socialized to unfamiliar dogs as a puppy, then she is probably not a dog that really wanted a companion all that much.  In my opinion, you also got your male TFT one week early.  I don't like to see a dog leave its litter before the END of the seventh week, and in some states it's even illegal to remove a pup before the age of eight weeks.  Largely, that's because they learn a lot about bite inhibition and the doggy social graces during that time.  That's not to say that had you waited your dogs would love one another.  In fact, dogs pick their friends, just like people, so the fact that you love both dogs will not necessarily mean that they will co-exist peacefully.  Personally, I don't blame Sophie - she is not a dog that has been used to physical rambunctious play, and now the poor thing has to contend with a puppy that she really didn't want.  I would say that if she is not willing to interact with him, that you discourage him from harassing her and redirect him onto some other activity, such as tug, fetch, chew toys, etc.  He should be in puppy class asap, so that he learns to have good doggy manners, both in terms of his obedience skills and his social skills.  If you can afford doggy day care, that might help, too.  He can tire himself out with dogs that like to play, and maybe not be such a pain in the neck to Sophie when he gets home.  Teach him "leave it" and "come" as soon as you can, so that you can direct his movements in the home.  
Here are some links that might help you learn more:
http://www.diamondsintheruff.com/multipledogs.html
A tape and a book that I recommend:
http://www.dogwise.com/itemdetails.cfm?ID=DTB900
http://www.amazon.com/Feeling-Outnumbered-Manage-Multi-Dog-Household/dp/18917670...