What Exercises Can I Do To Build Up Strength Prior To Mastectomy?

What exercises can I do to build up strength prior to a mastectomy? My mastectomy will be in 4 months when I finish chemo. I have reasonable strength - 10 full push ups, 40 bicep curls with a 15 lb weight. As I am relatively active and need to be able to take care of 100 lb dogs and reel-in a 35 ft power boat, I am very concerned about loss of strength in my primary arm. Thank you for your guidance.