Hi Susie,
XCHT is exactly how I'd start, because of it's tremendous reputation in dealing with splenomegaly.
That being said, runner ups would be Liver Qi movers and even Blood movers, given this breed's tendency to Liver Qi stagnation and Liver-Spleen disharmony. Xiao Yao San is often helpful in these animals. If things are really lumpy, I'd consider Ge Xia Zhu Yu Tang. It can be used with XCHT if desired.
Hope that helps you out!
Steve