Will my 11 yr old daughter remember the German language she was fluent in her first 5 years of life?

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Hello, my daughter is now 11 years old. I am German and her dad is American. For the first 5 years of her life we lived in Germany and she was fluent in German but not in English. When she was 5 we moved to the US and from then on she was only surrounded by American English speaking people, unfortunately I did not keep speaking German to her to keep her fluent in the German language. Now she is 11 and seems to have forgotten most of her German language skills. We will be moving back to Germany within the next few months and my question is if she will regain some of her German language skills with time or will she have to learn it all over again? Most people tell me that it won't take her long to remember German since she was once fluent.