Female to female aggression

Question
Good day,

I am the owner of three bulldogs (all rescued).  I have 2 females aged approximately 5 and 2, and a male approximately 3.  The 2 year old we rescued in September, and since then, we have had aggression issues with her attacking the other female.  

The other female, the 5 year old, is spayed and the younger one was just spayed yesterday (we were told by the person surrendering her that she was, but do to having a scar for a previous c-section, this was not confirmed until she had a heat cycle).  

We were hoping that once the spay was performed, the aggression would drop.  However, it has not as of yet.  Therefore, we we wondering how long after being spayed does aggression usually manifest itself as severely as prior to the procedure?  

I know that this is not a "magic pill" to stop it completely.  But we do hope that it will lessen the aggression.

As an FYI, the behavior is usually triggered by things such as loud noises that produce excitement amongst the dogs (like a knock at the door or the garbage truck outside) and giving attention to the older female.  we were also trying dog appeasing pheromones as well to help the issue.

Answer
Two females might develop antipathy toward one another and this is almost always rank related.  However, your new addition might be demonstrating referred aggression created by general hilarity among your pack (by various stimuli which produce excitement.)  Spaying any bitch will not in any way affect or change this situation and, even if it were to help, it would take months for hormone levels to drop.  You've already been lied to by the former owner; it's possible that this female to female aggression is the reason they wanted to dump this bitch to begin with.  Put the new dog on long, strong house tab (leash) and carefully monitor her interaction with the other female.  Do not allow her to greet people at the door or interact freely with visitors, as this is rank promoting.  Female to female aggression can quickly escalate and is quite difficult to extinguish.  Both females need to be evaluated for temperament and you need a rank reducing protocol put in place.  I suggest you hire a certified applied animal behaviorist with experience in female to female aggression problems.  You need to be instructed on how to obtain psychological dominance, how to use positive reinforcement training to control all your dogs at once, and how to read body language so you can ascertain what might be about to happen and thereby reduce any further expression of aggression between these two, before it develops into a fight on sight situation.  Contact the veterinary college in your geographical area and ask for referral to a Ph.D. or DVM.  Meanwhile, closely monitor this situation; remove (with the house tab) the younger bitch if she demonstrates any untoward aggression toward your older female.  Simply take her into another room for a minute or two, then reintroduce her while holding on to the end of the leash.  It's impossible to determine what the cause of this behavior is without seeing it, so an in person consultation is absolutely necessary.