just you two, or even go on a trip. Just be mother and daughter. Reminisce the "good old days" whe she was the only child. Do things only mother and daughter can do together. Disney is OK, but do a long walk on the beach.
Her sense of self is the issue. She needs to feel the existence of herself, apart from others, that has rights and responsibilities. You can watch Joel Osteen on TV or Youtube with her every weekend. Most people who watch him are not Christians.
Give her a big hug everyday and say "I love you." Let her feel your love.
Treat both of them in the same manner and voice. Do not compare them. The eldest child has her special place in a family.
Consider getting a pet, even just a gold fish, and ask her to take care of it. Before she can know what others feel, she has to know what her own feelings are.
Have her stand in front of a mirrow and describe herself.
Ask the town librarian for children's books on character development.
Do not push her to be social now; her problem is more basic than that.
Stop making demand. See what you can do to help. "I got you an electric tooth brush. Want to try it?" Lift the water tank cover, "want to see how it works?"
Do not show your own anxiety.
