In medicine, there are some things that it's best to assume that the patient is either lying about or unaware of. Pregnancy is one of them. For example, any woman (and by woman, I mean anybody who has experienced menarche) who presents to the ER with lower abdominal pain gets, among other tests, a pregnancy test to help rule out an ectopic pregnancy, which can be fatal if not treated. Even if it's not such a dire situation, the earlier prenatal care starts, the better for both mother and child, and if the patient decides that she wants to terminate, the earlier it's done, the safer it is. I have seen kids as young as 12 gets tested; the youngest I've seen come back positive was 14, and she swore up and down that she wasn't having sex, as did mom and dad.
Given that the consequences of not doing one can be catastrophic for both patient and care provider, it's worth a few minutes of being pissed that one's integrity is being called into question.
Tell your friend that she needs to read the Patient's Bill of Rights (yes, there really is such a thing) for her doctor's practice; it usually states in one way or another that the patient gets to participate in any treatment decisions.