the scary part is that if she never found out who he was then she may probably had a crush on him.
she'll try to deny it and push such feelings aside but in the end she would be forced to accept them, ergo, the later she finds out the truth the worst it'll get.
I mean, can you imagine the sheer horrorific realization if she found out too late for her to get rid of her feelings? that no matter how hard she tries her feelings for the boy persist and don't disappear at all? that she slowly would feel jealous about girls getting close to him regardless of the situation?