Girls of that age are often shy their bodies are changing and they are becoming Women they dont always understand it, especially buying intimate things and going out I think you need to let her just be herself I doubt very much if she has a mental problem like your sister in law but if you are concerned go to the Doc for an evaluation, to me it reads like she is just becoming a Teenager.
I took my daughter to see psikolog last year and the result was 'low self confident'. . My husband is also a quiet and introvert person-just like my daughter. One of my sister in law is suffering scizophrenia. So, I really confused wether I should take this seriously or not.Thanks for your advice, I will focus on child anxiety
I suspect your daughter is suffering from anxiety (probably social anxiety). You might wish to google the term "childhood anxiety" or words/phrases similar to find more information. There are many books and internet sites which can give you additional information. Also, it might be wise to discuss this possibility with your daughter's family physician first and then her teacher. The teenage years are especially difficult for children suffering from this disorder. The treatment of this condition will depend upon the severity of her issues. If severe, your daughter will require medical intervention (perhaps a mental health specialist with experience in anxiety disorders). Anxiety is an inherited trait, a very common mental health issue for children and teenagers and highly treatable. I wish you the best ...