My daughter is only a sophomore, so I’m not sure I have a ton of sage advice, but she did apply to a selective summer program this year, so I know the angst of the process and watching and waiting to find out about the outcome. My DD ended up getting lucky and got selected, but we spent a ton of time talking about her options if she didn’t get selected - how else could she pursue the language she was interested in, what else could she do if she decided to reapply, and what else she could do with her summer if she stayed (travel, hang with friends, do her swim season, etc.). Both of my kids are super involved in sports, performing arts, and leadership and both have failed to win a race, get a part, or win an election a ton of times which I know has helped them not get too invested in long shot opportunities. Sometimes these selective summer programs are even tougher for kids who are young for their grade (my DD has been waiting for 12-15 months to be old enough to apply to NSLI-Y), so maybe reminding her of that will help too.
Overall, I think everyone has given you some great advice about crafting her own unique summer experience based on her interests, but I also think working with her to better deal with disappointment will be a great life skill for her in the future. I know from experience that perspective can be tough if your DD is lucky enough that her life has been pretty loss-free and easy-going to now. While I grew up without money, I also grew up without extreme loss or tragedy and had a pretty blessed life, so it took me a while to develop resilience in my teens/young adult years. My kids, on the other hand, lost their dad (my husband) at young ages (9 & 12) and they seem to have the perspective of full grown adults. They just know nothing is ever that bad and in some ways, it makes it easier for them to try for things that are long shots for them. Obviously, perspective comes with time (or experience in the case of my kids), but I wish that I had the perspective my kids have now when I was a teen.