You don't want to update constantly and I agree with above that this isn't an accomplishment that's likely to make or break a decision. Keep a list and update with multiple things at a time, as needed.
I wasn't planning on updating "constantly" but providing this single additional piece of information, which we would have included in the application if it had happened a few days earlier, to application files that are still being assembled and well before the deadline for the applications to be reviewed. They are all waiting on at least her DE transcript and, in most cases, recommendation letters. IMO, it is much more like providing the transcript from an additional program than wanting to add a book to a book list every time she reads something. This is a major change in status for one of her primary volunteer/community service activities, in moving from volunteering to being invited to be one of the two paid leads for that situation, something that is not typically offered to a highschooler in that institution.
I honestly don't expect this to impact admission decisions, but think it could be a factor in scholarship competitions/decisions. Her GPA and test scores put her very much in the running for top merit aid at all the schools (up to and including a full ride), but that aid is not automatic. I realize that most of these decisions will hinge on scholarship weekends at most of the schools, but some of the schools in question do not have those or a separate scholarship application.
So, that brings a question. You mention "multiple things"---what types of things are generally considered worth adding, other than receiving a national award? At what point in the process would you suggest sending in such information? If her application was already complete and being/had been reviewed, I would probably see it as something to include with the end of semester grade updates, but that's not the case.