My 18 yr old daughter is thin, exercises and has a healthy diet. Her LDL is at 143. Positive family history. What can she do now to lower ldl?

See below. I agree with dr. Diamond but would also suggest working with a nutritionist -- often they can suggest ways to cut sources of fat and cholesterol in her diet that you and your daughter may not have thought of.
Not many good answer. Excercise is helpful, as is a low fat diet. Supplements such as fish oil may help. There are unfortunately genetics conditions where the body does metabolize the fatty material well, leading to elevated levels. Medication may be a needed, last resort.