Can I act as a representative for a POA?

My mother is power of attorney for my grandmother. When my grandmother's health began to fail, we had to admit her in a skilled nursing facility. My mother, the POA, was unable to commit or help in this and I took over the role of admitting her. I reached numerous dead ends as I'm not the POA and my mother has not been cooperative in helping me. Rather than petitioning the courts to get guardianship or have the POA transferred to me, is there a way I can serve as a representative to the POA or act on her behalf? I do not want POA permanently for when end of life decisions need to be made.