If someone had an abortion at 6 weeks pregnant, would her obgyn be able to tell or would he think she had a miscarriage? my friend is afraid to tell.

Possibly: it depends on how soon after the abortion she is examined by the other physician.

Ob/Gyn would not: If your friend had an abortion without complications, then her ob/gyn would not be able to tell just by examining her. However, if she is afraid to tell her ob/gyn, then she should find a new one. Patients should feel comfortable discussing all of there health history / issues / concerns with their clinicians without fear of embarrassment or humiliation. 1/3 of women have an abortion by age 45