Will I need a notarized letter from my 14 year old daughter stating her preference to live with me to prove my custody case?

A notarized letter will not help. If there is a court ordered parenting plan, unless the other parent agrees to let you move, you will need to file a motion to relocate with minor child before you can move. As part of the case, you can ask the court to interview the child (which takes place outside the courtroom with the judge). It will depend on the judge if they will interview a 14 year old. If they will not, you also could get a child and family investigator appointed so the child's opinion can be heard (through the CFI). Removal cases are very complicated and you should speak with an attorney about your situation if you are going to try to move and the other parent is going to fight it. Hope this helps. You can reach Dave Rich at (303) 886-2516 or dave@flatironlegal.com. Dave Rich is an attorney licensed in Colorado. Answering your questions does not create an attorney-client relationship between us. You should speak with an attorney to whom you have provided all the facts in your case, before you take steps that may impact your legal rights. I am not obligated to answer subsequent emails or phone calls unless you have hired me. I wish you the best of luck with your situation.