Is she lying about being on the pill?

There is this 23 year old woman that I know who has had two abortions in in the past 4 years. She said that she was on the pill both times. She is a very promiscuous woman and not exactly the most responsible person, but I find it hard to believe that she was on the pill both times. My feeling is that she most likely forgot to take it but is too embarred to admit it. What do you guys think? I mean how likely is it really to become pregnant twice while being on the pill?