HELP: Problem with dog aggression

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My wife and I are in need of some advice. We have a 14month-old CzW, and in the past few months, she's started to show aggression towards certain dogs. This has quickly become a problem as she's now bitten three dogs. In all cases, the dogs are VERY submissive (one was a female Blue Heeler, one a female Poodle, the other a male mutt). Other than their submissive nature, there seems to be no connections. She has shown aggression towards some other dogs as well, but, again, there seems to be no common thread between them.

How do we deal with this?

Some background:
Emma (our CzW) has been with us for a year now, and we have always heavily socialized her. She is around dozens of dogs each week, going to training classes, to the dog park, to the beach, on walks. This agression used to come up once a month, but now it's about once every 10 days that we see her be aggressive towards another dog.


Any help or guidance would be greatly appreciated, as we would like to stop this, but we cannot correct it until it happens (which doesn't happen often enough for a proper lesson).
-AM