My Senior Dog Has Mast Cell Cancer And Has A

My senior dog has mast cell cancer and has a tumor in her groin area. She is on the end step down of prednisone. Tomorrow I was supposed to give her i/4 of a 20 mg tablet every other day. The tumor has grown from walnut sized to lemon sized. My vet's office is closed until Monday because everyone is at a conference. Should I increase the dose now, or just wait until my vet is back in the office? I can't afford the emergency clinic at this time, so I hope you can advise me. Oh, my dog is also taking 50mg of diphenhydramine twice a day. Thanks a lot.