I think it's great that your friend takes such good care of herself, and reflects on different things. Although i do not think that an IUD would be any more problematic for a person with CP than any other women who has a foreign object inserted into her body, and whatever complications that can have. CP is not in the abdomen, and even so, it's impossible to push it out. I must say though, that it can fall out, but the risk is there for all women. But all of these questions is something a doctor can answer, and most likely also the concerns of your friend in relation to her CP.
I wish you and her the best of luck, in the pursuit of a happy and safe adult life