User blog comment:B214/Question and Answers 6/@comment-73.46.6.122-20160729165607/@comment-9595671-20160729235220

I'm pretty sure she and everyone else were told about the Raynare curse because almost if not everyone showed dissapointment in Issei since they felt he didn't understand Rias' feelings. Telling them would let them realize why he couldn't, especially since Issei wasn't sure why they were angry at him.

I'm pretty sure Rias actually did try to help them, but unfortunately realized she didn't know how to help them truly heal because she didn't have troubled pasts like they did. Even in real life, sometimes there's someone who can do a better job at helping a certain person because they understand their situation better.

I think Sona herself gave a good example of this as she while she also lacks a troubled past and she tried to help Rias with her problems to little success, she managed to dissolve her own planned engagement without help, and didn't know how to aid Rias who im comparison lacked the same options and luxury she had.

It's like you said, Rias is simply a high school girl. Just like a highschool girl would be confused about love, they'd be confused on how to help someone with an issue they'd been been dealing with for a long time unless they had a similar experience or udnerstood their feelings.