Ok ... this is getting messy ... you say she was a dependent in 2018 AND has not filed the 2019 return yet BUT she got the stimulus money. SO for her to get the stimulus money she HAD to have accidentally OR on purpose filed the 2019 return using the NON filer registration program. Since your return got rejected due to her filing already that is the only logical conclusion.
NOW you must BOTH amend the returns you filed. Yours to add the child and her's to remove herself.
