Usually those racket mechanisms are pretty low tech. It is possible it simply failed, presumably partially before she got in (the article is not clear on if it

Usually those racket mechanisms are pretty low tech. It is possible it simply failed, presumably partially before she got in (the article is not clear on if it only "clicked" once because she was too large for it to click more, or if it only clicked once when pushed down the normal way. The first is probably easy to alarm on, the second less so). The second should have also been caught during some sort of inspection....