My 11 Year Old Lab Mix, Alice , Seems To Have Developed A Large Abdomen Recently, Why?

Last summer Alice had surgery to remove a cancerous tumor on her hind left leg. The vet was not able to get it all, but it doesn't appear to have grown back. Today I noticed how large her abdomen is. Her eating habits have not changed, but she has been moving slower, she has arthritis in her joints. Her belly is not hot, red or tender to the touch. Our yard is all dirt presently due to a remodel. Could she have picked up a parasite? Her b.m.s are normal. Any ideas to take to the vet?