Not graduated 18 year old moving on to YSA

What would be recommended when an 18 year old has one more year of high school while the rest of her class is graduating and going on the the ysa ward. Her maturity level allows her to fit in better with an older class and if she stays she will be in the Young women's class with the 16 year olds. She is wanting to move on with her older class instead of being stuck in young women's for another year until she graduates. What can be done for her?

Times like this, I look in the General Handbook. I'd start with 11.4. Given that she should be in RS by the time she turns 19, that's probably going to limit holding her back. That section also describes how the decision is made.

This doesn't look great either way. If she stays back, she'll be with 16 year olds. And while I understand the desire to "grow up", if she moves on, she'll be the only one still attending high school when her peers will be either working or in college. Would she rather be the "senior" or the "kid" of her group?