I would see an elder law attorney regarding this question. If there are no papers, no proof you were actually raised by this woman, you may have no standing, and she may be in the care of the State who will appoint a guardian Fiduciary if she has made no papers while she was competent to do so.
Your options for your State will be be presented by an elder law attorney. Take all proof of your relationship to your stepmother to the meeting with him/her. This may include letters and affidavits by people who know all of you and your history.
Where doe Stepmom reside now? Is she incompetent? Who is managing her care now? Does she had a friend or acquaintance who is her POA? Guardian? Conservator? Is the state involved in her care.
Where is her care being administered at this time, and how? And by whom?
As step-children was she a mother to you or in your life growing up. Or was she married to your father after you became an adult? So she is just Dads wife. How close are you to this person? Because it will depend on how you handle it. If you do not want to be involved in her care, then call APS on a vulnerable adult. If you want to be involved then I would get POA. If she still understands what that means, then a lawyer may draw up the papers. And in this situation, I would use a lawyer. Next would be guardianship. If you win, you may be able to use her money to obtain it.
You don't give enough information but if no one is her PoA then you will need to either pursue guardianship through the courts or call in APS for her county to report her as a vulnerable adult and then the county will eventually become her legal guardian and her stepchildren won't have any caregiving or management responsibilities anymore.
Who is "we"? Stepkids? Friends? How old is she? How bad is the memory loss? Is she officially diagnosed with dementia? Does she have her paperwork in order and have someone designated as POA?
Your options for your State will be be presented by an elder law attorney. Take all proof of your relationship to your stepmother to the meeting with him/her. This may include letters and affidavits by people who know all of you and your history.
Where doe Stepmom reside now?
Is she incompetent?
Who is managing her care now?
Does she had a friend or acquaintance who is her POA? Guardian? Conservator?
Is the state involved in her care.
Where is her care being administered at this time, and how? And by whom?