This is a non-issue for many reasons, least of all that no admissions officer will view SYA as “less rigorous.” That said, SYA is not for all students. In particular, from an academic standpoint, students advanced in STEM are better served, IMO, staying at the home school.
There may be other valid concerns, including rejoining EC’S at the appropriate level upon return, and getting in her graduation requirements (most often an issue with USH abd science). And I’m not sure the BS she attends as a sophomore will allow her to repeat a year at their school. But I guess that’s a school question. A PG year at another school might be an option if the current school does not allow her to repeat