I'd suggest giving her the chance to say whether or not she has a problem first. Ask her outright, 'is there any concerns or problems you want to tell me?' and then, if she says no, and you still don't believe it, tell her of your concerns. she may appreciate the respect you are giving her, rather than accusing her striaght out or assuming.
i only say this because this is how it was handled in my friends family, her mum was worried, and my friend confessed to it.

best of luck