Lactating Daughter?! she had been doing this for over a year

Hello everyone, A week or so ago I found my daughter who is turning 16 next month lactating into a bowl in her bedroom. When I walked in on her she quickly covered herself with the bedsheets but accidentally tipped the bowl over onto her bed. When I asked why she was eating cereal in bed she confessed that it was breast milk. She later told me she had been doing this for over a year and she was too embarrassed to tell me. I of course made an appointment with our GP who explained that it had only persisted due to the regular stimulation from her emptying her breasts but she could not explain how it had started. My daughter says she is still lactating and it doesn't sound like she is interested in stopping.I am awfully confused about how this happened and if she is enjoying it how do I get her to stop?