Pain in arms/shoulders. Muscle injury.

My mother is facing left hand pain since 2-3 months now.Some days the pain is just on hands above and below elbow.Some days it shifts to shoulders and area just behind shoulders.On some days it moves to front area.just above the breasts.And what we have observed is if she rests them,pain goes away.Any minor repetitive movement done with left arm(e.g:dusting done with a long broom made from bamboo or carrying grocery shopping bags weighing around 3-4 kgs) triggers pain which was stopped and then pain continues for 3-4 days or even a week.An elbow support belt helps reduce pain.We monitored her blood pressure,pulse rate & body temperature through thermometer.Everything is normal.She takes a walk everyday for 30 to 45 mins every day.No breathing issues during brisk walking or climbing stairs.no chest pain while walking or climbing stairs or performing any household chores.Doctor please help..We are confused if it's related to heart or breast cancer related or any left arm muscle injury.