963 Haha! Just saw your profile picture, didnt realize it was you guys! Cheyenne can be quite assertive in her “active submission”. I think you are hitting the nail on the head that Slate just has enough.
I personally would stay away from the dog parks – it is only a matter of time before a dog does more than a growl if she is not reacting. Socializing is good, but “play dates” with dogs you know are better than the “roll of the dice” you will find in the dog park.
I think mainly you will have to catch up on the “leave it” with Slate and be ready for Cheyenne on the walks and give the “leave it” when she is even thinking about it. You may have to experiment as to what training collar is most effective for this without causing unnecessary stress.