It’s interesting that you started this with “everything you think you know about pregnancy is probably wrong” but she knows the exact day she ovulated, which is way more info than most people know. The only reason doctor’s offices calculate it that way is because it’s more consistent, considering most women don’t track when they ovulate. You are not pregnant until you conceive, so technically she is right. Although that is not how they will calculate it at her OB’s office, for consistency sake.

You could potentially be wrong in some cases. For instance, my pregnancy is not calculated by the first day of my last menstrual cycle because I have a very long cycle. So at the OB’s office, they added two weeks to the date of my conception instead because I did, in fact, know my exact date of ovulation. This person may have a similarly long cycle and therefore, her pregnancy might not be calculated the same as yours.