I don't remember that she could do it online, but the school information is online. Once she got the letter she signed it and uploaded it or emailed it, I know I had to scan it for her. Then on her portal there was a copy of the letter of intent and her status change from offer to 3 schools to accepts at one.
Remember cadet command is accessible. If you portal updates and you do not receive the letter close to the date (everyone has the same date due so it will be posted on this board), you can contact them and they will help you.