Check with your local school district. I’m sure you could ask about fluency and for her to take a written exam, show a writing sample for usage. This will help you decide which middle school/HS Spanish class would be best for her when the time comes, if any. The Spanish teacher may be able to give you materials she can work on to get her written skills on par with her oral fluency. This could be a summer project for your D, IF she shows interest. When in HS she can then be in an appropriate class. Or she could start a third (after Spanish and English) language. Learning a different language in the school setting is useful in knowing how languages are structured.
Her oral Spanish is likely filled with colloquial usage unlike the standard taught in US schools. For example, I have learned from highly educated neighbors that Puerto Rican Spanish can be difficult for other Spanish speakers because of the shortcuts they take with words et al. American English is different than British and other places’ English.