Would she consider a women’s college?
Scripps is the one, IMO, that hits virtually all of your parameters. Even though it is small, it effectively functions like a subdivision of a mid-sized university, as there are around 7K undergrads in the Claremont Consortium, with all campuses in an immediately-adjacent, walkable patchwork of different architectural styles. Students seamlessly cross-register on a shared portal for classes throughout the consortium, and participate in shared EC’s and athletic teams. (The shared student newspaper is particularly good, and a great social incubator as well.) Plenty of guys around, both in classes (all classes will be mixed-gender except for the three semesters of Scripps Core humanities) and out. They get so much sun that even a SAD sufferer may begin to hope for clouds, lol. No Greek life, but a lively party scene for those who want it (most parties on the other campuses, meaning one can enjoy but walk home to relative peace and quiet). “Wide liberal arts” is exactly what they’re good at, with strength in both humanities and sciences, and dual majors more-or-less the norm.
Other women’s colleges hit many of your criteria as well. Smith is particularly strong in STEM (as well as humanities/social sciences); but there’s more separation of the consortium schools there so it may feel smaller than your ideal. Same with Mount Holyoke (which has many of the same attributes but a bit less STEM focus). Barnard fits in every way but the acceptance rate, which only tops 20% if you apply ED. Bryn Mawr and Haverford have a combined population of around 3200 (80% female altogether) - the other consortium schools (Swarthmore and UPenn) are much more separate. (And lastly Wellesley - acceptance rate is in the teens and population is around 2500, but deserves a mention for academic strength, plus cross-registration at MIT and other area schools.)