I am a doctor and based on my years of experience I can tell you for sure that I have no idea whether she lied to you or not. However, this does happen to some women. The hymen is a fragile tissue that can easily rupture in the past due to strenuous exercise, trauma, cycling, etc. Some women may not even know it because they were too young at the time.

Since many friends have asked about this issue, I would like to give my advice to the netizens: Using the first bleeding to "determine" whether a virgin is a virgin will unjustly accuse some women. The damage is done as soon as you "question" her. Whether a woman is "chaste" is essentially just a concept. Moreover, the first bleeding does not necessarily mean "chaste". I suggest friends who are concerned about the "integrity" of the woman to read the discussion of "chastity" in "On 'Hymen Plastic Surgery'" by Mr. Li Ao, a Taiwanese writer.