Yorkies who fight

Question
I have a 9 month old female yorkie puppy, and two months ago I got a 2 year old yorkie female.  The two year old is pretty laid back, but for some reason the two of them will suddenly begin a violent fight and will not stop no matter what we do.  We are afraid they will either hurt each other or we will hurt them trying to break up the fight.  What should we do.  The two year old was in heat about a month ago and we think the puppy may be in heat now.  I was waiting until the puppy is a year old to have them both spayed since the puppy is only 4 lbs.

Answer
Julia,

Interdog aggression is a very difficult problem to solve.  Typically it is male-male or female-female. It is unusual to have a puppy involved though, and I worry that it will escalate with time.  Usually, the two dogs fighting are both mature adults.

I would try to get some professional help on this issue as soon as possible.  First I would visit your veterinarian and see if they can help.  If that doesn't work I'd ask for a referral to a good trainer.  

Unfortunately, behavior problems can be very very difficult to solve.  Be patient...  Keep the two separated for the time being.... And get some help.

Good luck to you.