I am so sorry to hear about your Penny. Please accept my sincere sympathy with the passing of your family member and best friend.

I don't know if this is helpful, but the only side effects I could find before putting our dog on it talked about diarrhea and vomiting.

Our Peach has a degenerative disease of the hips that will eventually end with our having to put her to sleep when she is no longer able to get up. She has had a lot of trouble getting around and the vet told us the Rimadyl would ease her pain and inflammation; it wouldn't make her problem go away, just ease the pain until such time. She's been on the medication for about 4-5 weeks and she seems OK.