sudden behavior change

Question
I have 2 soft coated wheatens, female almost 3 yrs old; male almost 2. Both were spayed/neutered in Deceember 08. We are starting to run into the female showing some aggression towards the male. He can be a cross the room, usually looking at her and she will growl and dart after him and fight with him. He does not have toys, food, bones etc... The female is also chewing the hair on her front legs.To give a little history; In June of 08 they had a litter of pups. No complications through delivery and 8 pups were born healthy. All were placed with very nice families. On occasion 4 of the "puppies" have been coming to our home for us to puppysit when the families go on vacation. At most we have had 2 at a time. Do you think this may be stressing her out? Does she sense that they are her puppies?

Answer
Your female does not know these are her puppies and it appears she is suffering from stress and anxiety and is developing an OC behavior (chewing her front legs.)  Her escalating statement of rank toward your male may be the result of having multiple dogs enter her space (even though this does not occur often), but it seems more to be a reaction to the male.  A dog making direct eye contact with another dog (even from across the room) can precipitate an interaction based upon rank opportunism.  I can't see that from here.

You need to do some homework so you can develop the knowledge and skill to read the body language of both these dogs.  I strongly suggest you read Turid Rugaas' book "On Talking Terms with Dogs: Calming Signals".  Equipped with this "translation" of dog communication, you will be able to determine exactly what is going on between these two dogs.  You'll have to make a consistent effort, after reading the book, in observing them quite carefully over the course of 48 hours.  You can even keep notes so you can refer back to your observations in order to determine just how often, if at all, the male is initiating a rank struggle with the female.  IF you discover that he is doing nothing, you must use your ability to read body language to determine what rank they both have in regard to one another: is he the more naturally dominant, is she, or are they of comparable temperament?  This is quite important because you will have to actively demote EACH DOG while, at the same time, promoting the most naturally dominant over the other.  You will need positive reinforcement training (a clicker, clear cue): go to ClickerTraining.com.   Train both dogs, independently of one another, to perform one behavior ("Sit" but use a unique word, something they have never heard before).  It will take approximately two weeks of consistent, short, daily sessions to obtain a solid response to your word for "sit" in both dogs, separately; you must get a 100% successful response from both dogs, every single time, to qualify them as having acquired the training.  From this point on, both dogs must "sit" for everything (this is called "Nothing In Life Is Free -- NILIF).  They must sit for feeding, being petted, going in/out, any and all interaction with YOU; this will psychologically promote you and should help your female to become calmer and less driven to control her environment.  However, here is where it gets a bit difficult: you must determine who is who BETWEEN THEM, also, BEFORE letting them in/out, greeting them, feeding them, because you must promote the RIGHT DOG over the other.  When you get to this place, REPOST with your observations and I'll try to assist you to determine who is who; if you are overwhelmed by this, get professional help by contacting the veterinary college in your area for referral to a certified applied animal behaviorist or go to this site which supposedly checks educational and professional credentials:
http://www.iaabc.org/

Meanwhile, put a strong house tab on the female so you can intervene should she charge the other dog, in order to avoid injury and what is most likely a rapidly deteriorating relationship between the two.  Say NOTHING and do NOT put your hands on either one, merely remove her using the house tab (do NOT get in the middle between them.)  You haven't mentioned what the male's reaction to this "attack" is, presumably he is fighting back.  If he is NOT but is attempting to get away, that's a clear indication that the female is reacting inappropriately.  I think you should bring her OC behavior to the attention of the veterinarian ASAP, while you're waiting for the book and before you attempt the demotion.  There are medications she can take that will alleviate her anxiety, stop her obsessive chewing and may help overall in your attempt to rehabilitate this situation.  In terms of allowing other people's dogs into your home, I understand why you're doing it but until the situation between your own dogs is resolved, I suggest you ask their owners to find other arrangements.