Explain to her that it's a very serious issue and if she knows she has a problem with eating then it should be seen to by professionals. There is the possibilty of her saying it for the attention, but it is important you don't rush to this conclusion in case something really is wrong.
I suggest you try and talk to her about it and just let her know you're there to support her.
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How to become immortal:
Read this signature tomorrow and follow its advice.