Our community college had gifted summer courses last year, but dropped them for this coming summer. I suspect insufficient demand from lack of good marketing - DD looked at the descriptions, said, "but I don't know how to do archaeology or geometry!" and flatly refused to consider them.
I'd do the CTY Chinese course, but it's $900. For that kind of money, she can practice with her grandparents. Heck, for that kind of money, she could have a one-on-one native speaker tutor all summer long, in the absence of grandparents.
We're doing Camp of Mom this summer. Singapore Math (as enrichment and depth, not necessarily to get ahead), Story of the World as audiobook, Singapore Science (again for enrichment), and language arts focusing on root words / puzzling out unfamiliar vocabulary and on writing (5 paragraph essay and research paper). DD is a good writer when she has a structure to go by, but flounders without one, so she's highly motivated to learn some structures to launch from.
