I quit my internship

I have been interning (no expenses paid) for the last four months with a lovely woman. I work really hard and she is usually very kind. I recently got diagnosed with ADHD and amongst other factors (poor mental health and inability to focus) I felt it necessary to quit so I could focus on my studies. I emailed her yesterday a very nice polite email and explained I needed to focus on my studies- she simply has not responded.

I’m wracked with anxiety that I did something wrong- and truly disappointed as I have been working for four months and in my opinion deserve some acknowledgement of that time.

I’m 21 and feel so worried about my future.