What Causes Shoulder And Left Chest Pain With Breathing Difficulties?

my friend has been up all night with pain on her left side, mainly in her shoulder and chest,she went to doctors today but was told she had a strained muscle in her chest, she has difficulty breathing and is still in a lot of pain, she doesn't have any other stroke type of symptoms, and doctor prescribed more Valium and a muscle relaxer but it doesn't seem to be working, is it possible that this is all it is, I advised her to ring an ambulance if she is still in pain tonight, but because we live on an island it can be difficult to come back home so that's why she hasn't rung them, she hasn't done anything recently that would have caused a muscle strain, so she is not sure what or why it is happening