It sounds like the JR is doing some resource guarding - the resource could be a bone, the couch, you and your salad, or all of the above. If the JR is on the couch and starts guarding (as soon as you hear her growl, or see her start to tense up and stare at the other dog), I'd start by just getting her off the couch as soon as it starts. When she figures out that guarding gets her thrown off the couch, hopefully she'll stop a lot of that guarding. At the same time, you should definately reward her when she does NOT guard - she's sitting on the couch and the other dog comes up, praise the JR a LOT, give her a bit of your salad, whatever, so that she learns that staying calm is the right thing to do.
When they're playing, it's a good idea to work on a lot of recalls - call one (or both) of the dogs to you in the middle of their play session, and then give them some kind of big reward when they quit playing and come to you - a good treat, a walk outside, whatever. Then do recalls periodically as they're playing, and do recalls when you see them begin to tense up just before they start playing too rough or fighting. That way hopefully you'll be able to stop them before they start fighting.