Can a nursing home bar a family member from visiting their mother and ask that they get guardianship before they can visit her?

I have a feeling Mom is a Ward of the State meaning a Judge has appointed a guardian. This means the guardian is in charge of Moms care. APS was probably called on Mom and they removed her from her home. How were u and sister contacted? Was someone living with her and leaving her alone?

Having issues in a nursing home seek the help of the local Ombudsman, they can assist you in obtaining answers. The National Consumer Voice for Quality Long-Term Care- Ombudsman Locator https://theconsumervoice.org/get_help

We need details for this case.
Why was the family member banned by the Nursing Home? Have they been causing problems during their visits?
Who is the POA for the patient they wish to visit? Has the POA forbidden visits? If so, why?
Under circumstances where a NH resident doesn't want visits the visitor can be banned. Under circumstances where a person causes problems when visiting, has been asking a possibly confused person to sign things, change things, do thing, the NH may ban the person. Under circumstances where the POA for the resident feels that the person visiting poses problems of abuse, fraud, and etc. the person can be banned by the POA.
So looks as though you are looking at a consult with an Elder Law Attorney to give him or her your details and find out what your options are.

I think a lot more detail would help people respond. Why is the nursing home barring a (or all?) family members from visiting? What rationale is provided for getting guardianship? Who placed the mother in the nursing home, and what were the basis, the issues and concerns?