Neither you nor your husband can do anything. As it stands, he does not have a daughter (legally) and has no rights to involve himself in her life without her parents permission. As his spouse, you have even fewer rights, which is impossible though becuase he has none at all.My step-daughter was adopted by her ex-step-father some years back. She has asked me to find out if she can legally change her last name to my husband's name. Is this possible without her mother's consent or do we need to go through the courts?
So, she is not your step daughter. You nor your husband can do anything to change the girls name, even with her mothers permission.
If anything, since you did not include any timeline nor much info at all, is to investigate the possibility that the adoption could me reversed. That would vary upon a lot of things, none of which you have included, or even sound like you know yourself.
or investigate the possibility of your husband adopting the girl but that would require the step father to relinquish or have removed his (the adoptive father) parental rights.

