Northern Virginia Writing Project had both Saturday one-day workshops and a summer two-week young writers program (hosted at GMU, not residential). Not sure if the program is still at GMU etc. but look them up. They were the Young Writers Project of NVWP but not (at that time at least) affiliated with the UVA program of a similar name that someone mentioned above. Things might have changed since my DD did their summer camp and workshops, though. (Don't let "young" fool you - these are for HS students too.)

I'm surprised no one has yet mentioned the Reynolds Young Writers Workshop at Denison University in Ohio. My DD did it the summer between junior and senior years and had a fantastic experience, both as as writer and as a person.

https://reynolds.denison.edu/

The Reynolds program is one week long but DD said she wished it were a month. We were all very impressed. Check it out.

Iowa Young Writers’ Studio

Young Writers Program, run by UVA, but housed at Sweet Briar. My daughter loved it, and as a teacher myself, I was very impressed.

Great suggestions. Thanks again.

University of Maryland has the Terp Young Scholars Program, which includes a creative writing workshop. I have friends who have sent kids to the program and they gave positive reviews.

https://oes.umd.edu/pre-college-programs/terp-young-scholars-campus/courses

Georgetown has a Creative Writing Academy.

https://summer.georgetown.edu/programs/SHS07/creative-writing-academy

Kenyon College also has a Young Writers Summer Residential Workshop for high school students.

https://kenyonreview.org/workshops/young-writers/

Thanks. Dd wants an in person workshop so sadly the Juniper institute program is out.
The Sewanee application seems to be more involved than the Bard college one. Does it mean it is more serious? How different are these programs?

Sewanee Young Writers Conference

https://new.sewanee.edu/sywc/

You might check out the Juniper Institute at UMass-Amherst. https://www.umass.edu/juniperyoungwriters/juniperyoungwriters

(Although it looks like it's online in 2022.)

I attended - long ago now, holy crap, in 2007 - and it was really fulfilling. Great staff and environment. Still keep in touch with friends I made in those weeks.

My DD, now a freshman, wants to spend a few weeks honing her writing and creating a portfolio. Ideally at a college or university.
We know of Bard college, Emerson college. If your DC has attended or if you know of any programs, I would be grateful for ideas and reviews.