Sister almost done radiation treatments for mixed ductal/lobular breast cancer. noticed that her breast looks dimpled. could this be from radiation?

Unlikely: Radiation therapy can cause some degree of scarring or deformity of the breast. But it doe snot develop so soon...it takes a few years for radiation related changes in the breast form to show. Therefore it is most likely due to prior surgery. Ask your treating doctors for better explanation of the changes in the appearance of her breast