You are correct she get one of her legs crushed it was planned by her mom. If I remember correctly her mom is the one who suggest to the emperor for her to marry the ml. Due her injury she relies
on incense to help her with the pain. From spoilers I haven seen from TikTok at one point she was pregnant but lost the baby bc it was still born and she "die" we are not sure weather she is actually dead or there a couple of theories on TikTok that the ml might have some power to turn time or see the future but I am not completely sure but he is in denial that she's dead. After news of her death  the crown princess suggest they get married again but he refuses and says something like do twins not understand bc for the crown prince he chokes him but he suffer pain due to the oath from the first empress that he has to protect the twins. Sorry if this all over the place but this most of the spoiler I have seen on TikTok and from I read up chapter 70 of the novel

Maybe