When she told her that the emperor's heart is the one you can least understand or the one you can least trust, I should have realized on first watch that this was not going to end well for Ruyi. And yes I've watched this show at least 20 times over the years
Rongpei added the stability to Ruyi that she needed. Somehow I don't see her being as meek as Souxin when Souxin was being tortured. One of my favorite Rongpei scenes was when she was watching how Halain didn't want to repeat what Jia said. She worded it so she didn't volunteer but was made to repeat Jia's words. Rongpei pays attention and realizes that the emperor must be handled carefully, especially if you want him to do something you want him to.
Ruyi is the most suitable candidate to be the future empress. Not only she doesn’t have an evil heart and care for her servants, she also has a good relationship with many other concubines.
Upbringing a child is very important. If the mom has an evil heart then the children will listen and follow the same path. In the end, you still get retribution in return.
Thankfully, not every child will completely follow for long, if at all. Some children simply have a clearer view of their heart and thus, a clearer view of the world. It is a priceless gift. Even if the parent/family can't appreciate them, those of us who meet with them cherish and hopefully, learn more.