If neither of you have taken the oath by your daughter's 18th birthday, she will not automatically get citizenship from you guys. She would have to apply for naturalization on her own if she wants citizenship, and she can N-400 as soon as she turns 18, assuming that she meets the requirements (has been a permanent resident for 5 years, etc., which she should meet if she got her green card at the same time as you guys, and you guys already meet it).