Peggy,
I have also had success with Albezia Complex (Standard Process/Medi-Herb) for anti-histamine effects.
Also, if you are having trouble controlling recurrence or swelling I have found it makes a significant difference to have E Zhu and San Leng added to the Xue Fu Zhu Yu Tang, so be sure you are giving the modified formula (I usually put 15 grams of each with 100 grams of base formula - or you can order it already modified). I am generous with the dosing of herbs in these cases. And when using strong blood movers chronically, keep an eye out for the development of blood deficiency.
Might I also suggest a healthy dose of Milk Thistle (20mg/lb/d) for its antioxidant and hepatoprotective properties. There is also some evidence of pro-apoptotic activity.
You should also assume you have GI ulceration even if there are no overt signs yet (~85% rate of GI ulceration in dogs with mast cell tumors even in asymptomatic patients). I recommend L-glutamine for all patients with bulky mast cell disease. L-Glutamine was shown in one human study to be as effective as carafate at resolving GI ulcerations. Also, consider Prilosec or pepcid, +/- carafate if needed.
Good luck!
Erin