I agree with GrannySu. Be very self-reflective and try to help her understand that "teenage angst" and set in before she is a teenager. She is going through a lot of hormonal changes right now and may even be feeling guilty about some of these new feelings that she is having. Talking with her and letting her know that these things are normal may help a lot.
It is not unusual for 12 year old to go through this type of thing. Often this is when "why am I here?"sets in. I found with my kids that it was helpful for them to know that EVERYONE goes through this type of anxiety -- it is normal. Sometimes they begin to think they are the only ones who are experiencing this type of thing and that there must be something wrong with them. My son (now 23) told me that he often thought there was something the matter with him because he didn't know what he wanted to do with his life. He had gotten the impression from TV, teachers, etc. that he should have a "plan" and he didn't know anything about how to go about putting one together. He is great at problem solvling, very logical and methodical, so the lack of understanding about this "plan" was very troubling. He had thoughts of suicide because he did not know what his purpose was, so logically, he must not have a purpose, therefore, why continue to exist? Very upsetting for me to hear about, but it helped me understand that he had a misimpression of how life was supposed to go at 12 or 13.
Try to have a heart-to-heart with your daughter, remembering back to when you were her age, and let her know that lots of people go through these feelings. If she does not have a diary or journal, now is a good time to start keeping one as the writing can be cathartic. Also encourage her to try something new that might open up other avenues for expression -- a pottery class, volunteer at the hospital or nursing home, learn a new skill -- one of my sisters took up woodworking.
Maybe the two of you can take up something more physical -- it is important that you don't let her take refuge in food. Take a look at yourself -- how do you handle anxiety? Now is a good time to be very self-reflective and show her by example that there are ways to deal with life's various problems.
Has your Daughter got friends is school okay ,is she happy to go there, How about some more Physical exercise , does she like a sport basket Ball Gym, or tennis,may be some activities she enjoys doing, perhaps the drwaing is a good thing and encourage her if she enjoys it ,If there is a Dad around could he get involved with Games and Fun.
I think your daughter is suffering from anxiety. If anxiety is the issue, your daughter will not outgrow it nor will it go away. In your daughter's case, one set of "fears" has been exchanged for another and then another. Until she gets proper treatment, I doubt if this will ever change.
Depression is often co-morbid with anxiety. If your family physician is unable to help your daughter, then ask for a referral to a medical person with experience in anxiety issues. Hope this helps ...