Some positive news

The positive news is that the culture the clinic sent to the lab to test for an immune related problem - came back negative.

The vet we saw today told us that there is still a possibility that Memphis has this disorder, even though the cultures were negative...but:
...she was in very good shape today for a pup with this immune disorder, especially one who hadn't had pain meds in 9 hours
...the Dr had only rarely seen immune mitigated poly-arthritis in a pup as young as Memphis
...she was doing as he would expect a dog with an infection would be doing, responding well to antibiotics

So, the plan is to extend the antibiotics two more weeks, not extend the pain meds and monitor Memphis along the way. If she has any more severe pain, we'll bring her to the clinic right away. If not, we'll call the doctor with an update each week.

If Memphis continues to do well, she'll be able to run around with her buddies on the last week of the antibiotics.