9 month springer spaniel bitch

Question
Our 9 month ESS bitch has been well socialised, attends training classes and socialises well with dogs when out on walks on and off the lead, although is often submissive when meeting dogs.She is yet to have her first season. In the past 2 weeks she has snapped twice at my friend's 2yr old unspayed bitch and once at another friend's 1yr old dog. This has happened at my friends' houses on both occasions. My dog does not have that regular contact with these dogs. In the case of the bitch, my dog greeted her excitedly on a walk at the next meeting. In the case of the dog, they had spent an hour together earlier that day sitting in a park on the lead. As young puppies they took part in lots of play fighting but I have noticed when, on the odd occasion we go on walks with these dogs, mine would now rather do her own thing. She spends a lot of time with a male neutered 2 yr ESS both at our home and my friends and we have had no issues. They play together, eat together and walk together.
This behaviour is out of character and would welcome any advice as to what might have triggered it and preventative steps.
Thank you

Answer
Your bitch is most likely close to going into heat and should be allowed to do so.  She needs the resolving influence of hormones released during the heat cycle.  She is most likely responding to increasing estrogen.  To spay her now would be to put in place this estrogen driven behavior, something you do not want.  Once she is well past her heat cycle (at least 8 weeks) have her spayed.

It's not uncommon for a bitch close to heat cycle to suddenly develop issues with another bitch (whether spayed or intact.)  This relationship might continue to deteriorate, or it may resolve in the next months.  I would not encourage this in any way; maintain this relationship while both are on lead or you may find yourself paying someone else's vet bill.  This is a clear indication that you cannot introduce another female into your home, at least not until you see the result (after months) of the spay.  This behavior does not indicate any problems with the temperament of your bitch, except that she is demonstrating a low tolerance level for others of her sex (especially if the appear equal in rank.)