Hi sanemom,
Is your DSD naturally introverted? If she is she might just need to re-charge.
Any idea what things are like at mom's? What is she having to deal with there?
This could be some kind of depression or anxiety. Have you talked with her about your concerns? Would she be willing to talk with a therapist? How long has this been going on? What was her personality like before? What kinds of changes have been going on in her life recently? Have you tried drawing her out by doing something she particularly enjoys? How's school been for her lately?
20 questions anyone?

- Just trying to get more of a feel for what's been going on
