I don't really see the issue here. If Sakurako wants to advance up the ladder she can still easily do it. Nothing stops her from studying more and getting degrees and who knows what else. Your college choice doesn't force you onto a unavoidable path.
The important thing is that Sakurako can get more successful if she wants, but she clearly doesn't care. Sending her to another college would have done nothing except make her feel torn apart from Kasumi and that just kills her drive even more.
When Kasumi kept her major a secret, it was so Sakurako would at least choose her main interest herself and that she did. Studying psychology is also something she only got interested in because of Kasumi in the first place. Saku can shine anywhere as long as Kasumi is around. And Kasumi also benefitted from Saku being at the same Uni (making friends, joining a club etc.)