Secrets (Never to be Told)

Lucy and Tim met each other at a bar ten years ago. They were drunk and he was desperate, leading to her coming home with him and having a one-night stand. Shortly after she found out she was pregnant, but she never got his name, nor did she see him again after that and she ended up raising their little daughter alone. On the first day of her new job, joining the LAPD as a rookie, she couldn't believe who was her field-training-officer...

OR:

Lucy and Tim made a drunken mistake and Lucy never told anyone about her daughter Hailee.