Hi Michelle, I would say that you speak English natively if you learned it as a small child. Are you familiar with the mistakes Chinese speakers make when learning English? My friend makes all those mistakes. She's well into middle-age, with grown children, and moved to the USA several years ago, speaking no English. Her Chinese education predates the Chinese government's emphasis on English training.
She doesn't understand pronouns properly, particularly he and she, and subject and object pronouns. She doesn't understand negation. The concept of verb conjugation is quite unexpected by a Chinese speaker if it has never been introduced in school. Her vocabulary is very limited. She doesn't use "to be". She doesn't use articles properly.
She's had no formal training in English. I helped her start with Duolingo but the product is not ready and it is not adequate. It has been completely ineffective. "Me very no happy", she would say.
My next idea is to find some effective self-study resources and try those. Then persuade her to upgrade her internet connection and try some individual coaching. I speak no Chinese so it is difficult for me to access, and judge the quality of, Chinese-based teaching materials.
Thanks