I’m Looking for a Book Whose Title I’ve Forgotten, Please Help, Thanks

I think the heroine's surname is Song and the hero's is Xie. There's a devoted second male lead surnamed Ji, who is the heroine's older brother but only appears later. The heroine transmigrates, and she and the second male lead are engaged, but I don't think the story ever reveals that she transmigrated. In the end, the heroine is a young lady of the Nangong family. Someone else is the young master of some mountain estate.