Aggression following traumatic experience - help?

[Natalie D]

MissMoneypenny is wonderful. We love her to bits. Super friendly, loves all people and well socialized with other dogs. Until last week...
I took her to the dog park (very regular occurrence) and as I opened the passenger door to collect her stuff and retrieve her from the back seat, a very large (prolly 80-90lb) black lab, who had apparently escaped her owner came out of nowhere and jumped in my front seat. Moneypenny gave a warning growl to let her know she was breaching her territory, and boom, lab attacks. Lots of snarling, big ole scrap. The owner came running over and we got them separated, but not before the lab had Penny pinned with her giant paws. Defeated, as soon as we were able to separate them, she jumped back into the car, went as far back in as she could and sat there wimpering. I sat with her for a few minutes, made sure there were no injuries, calmed her down with some love, and then we entered the park. No issues with the other dog...all seemed well.
Ever since, however, Penny has shown new signs of being very territorial - starts scraps when other dogs come around when she has a treat/food, and won't let other dogs approach me (whereas before, she would come and inspect other dogs if I were petting them all friendly like, now she growls and gets inbetween before the dog can even reach me). Just generally more on edge when around other 4-leggers. Still a-ok with all people.
Has anyone had experience with this kind of thing? Is it a passing phase, or are there things we can do to help her through this?
We were considering trying a doggie daycare once a week, but now I'm not convinced we'll pass the initial trial run...help?

[Patty, Roxy & Spencer]

When Spencer was about 11 mos. old a pit bull mix attacked him at the dog park.  He fought back and actually nipped the other dog's ear.  The next day we went to another dog park we liked and he wouldn't leave our sides.  Soon after we were at a beach house and he nipped a neighbor's ankle as he was entering the yard where we were.   He started showing other aggression to other dogs also.  I was going through treatment for breast cancer at the time which was upsetting for the whole family and I think he was picking up on this too.  I finally sought out professional help after he lunged at a woman with a baby carriage (a baby on board!) as she passed us when we were out on a walk at the park.  She startled him and luckily he didn't connect with her or the baby!  I wouldn't wait like we did.  I think you should seek out a professional trainer and get an evaluation.  We are still working with Spencer and he is almost 3.  We do take him to day care, but if they put him with other dogs he has to wear a muzzle.  On our walks we go where there are not too many dogs and work heavily with treats when we do meet one.  The big dogs are his main fear and sometimes the treats don't even work.  But, we keep working on it.  The trainer we worked with was great and showed us some great ways to work with him.  It just takes a long time and maybe he will never be able to play freely with other dogs.  Our other doodle Roxy is fine.  They have a great relationship and he trusts her.  The day care usually only puts them together, but he still is around other dogs even though he is in a crate observing.  Don't wait to get your pup the help she deserves to get through this trama.  Hope this helps.

[Natalie D]

Thanks for the insight - we've really been monitoring her behaviour, she seems to be recovering quite well. We're making sure she gets plenty of exposure to other dogs, and has been showing less and less signs of aggression. No issues at all this week! I took her to the daycare for an initial meeting - she did well, just need to work on her using her mouth/teeth during play now - but no aggression at all! :)