Hmmm. I'm not too sure what to tell you here. Have you talked to her about your "doubts"? After a surgical abortion, you should not have sex for 2-4 weeks. (not one week). In fact, you shouldn't put anything "inside" including tampons.
Her story does sound a little strange, though. What kind of "infection" could she have gotten from pregnancy? And they don't do a "surgical procedure" to check for cancer, but you can bleed a tiny bit. And is she claiming that lifting something heavy caused her miscarriage? What did the doctor say about this "infection"? Is she on antibiotics for it?
I wish I could help you more, but you really need to sit down with your girlfriend and talk about all of this with her.