In the words of the vet

FYI first: Intestinal lymphoma comes in two flavors. One doesn't respond to treatment, the other will maybe go into remission for a year or two with the meds she mentions. Neither is very good news.

Now to the cut and paste:
This e mail is intended to briefly re-iterate what we discussed on the phone.  If Cleo 
does indeed have an abdominal mass, and given her previous history, it is highly likely 
that she has intestinal lymphoma.  A more definitive diagnosis may be possible by 
ultrasound and aspirate of the mass.  Ideally this should be performed by the 
specialists at Upstate Veterinary Specialties in Latham.  We do have Ultrasound 
capabilities here, and we can try to obtain the aspirate.  Just keep in mind that we are 
not specialists and the detail on the ultrasound is not the same quality.  The cost at 
the specialists will be around 400$, if an aspirate is performed it could be 550$- 600$ 
(roughly).  The Ultrasound with Aspirate here would run approximately $400.  If you are 
interested in pursuing this here, we can schedule it for this Tues or Weds.
If you decide to not pursue further testing, and if the diarrhea persists, and/ or she 
becomes inappetant, or vomits again, You can re-initiate the prednisolone.  Start it at a 
lower dose initially, 5 mg once a day.  If she does not break with an upper respiratory 
infection and if she doesn't respond like we hoped, we can increase the dose.  If she 
does respond well, and if she has a persistent abdominal mass, we can discuss 
adding on Chlorambucil (Leukeran).
I hope this helps.  I really hope that the metronidazole does the trick and that the 
mass was just some fecal material.  Please keep me posted.
Jane