I need help with opinions of a camera for my granddaughter. She will be a freshman next year. She is very studious, an excellent student, and has great social skills. Last Christmas I let her take my Nikon D7100 to take pictures around the house. The images were startling in their composition. She took ordinary things and by perspective, angle of view, etc. and made them visually very interesting. They became art. She was very excited about what she had done and told her counselor she wanted to sign up for a photography class. She has been talking about photography since Christmas. I told her I would get a camera for her birthday (Aug. 28).
I don’t want to spend the money for a D7100. I also recently bought an Olympus OMD EM10. I have found this to be a good small camera. I want her to try the D7100 and the OMD EM10 and see how they feel to her. If she prefers the D7100 I am thinking of a used D5100 or affordable Canon’s. If she prefers the OMD EM10, which I think she might prefer, I am thinking of small 4/3 cameras including the OMD EM10. I want to keep the cost to around $600. I do want her to have an optical or electronic viewfinder and interchangeable lenses I will purchase if she needs them. (OK, she’s my granddaughter—not needs, but if she wants them.) We live close to each other, she has no father in the home, and I can help her since I see her every week.
Do you have any comments, suggestions, etc. about my thoughts and what is appropriate in terms of cameras? I would like a camera she can grow with.

Thanks for your help.
Terry