If the patient can talk, medical people tend to disregard a medical POA, insisting on the patient being able to make their own decision.
an avenue of less resistance is make friends with the hospital’s patient advocate. Notify him/her when you take mom into the ER, and communicate directly with her.
UTI’s generally resolve themselves if it’s minor. Cranberry juice and lots of it. Back to ER if fever. much easier than dealing with diarrhea from antibiotic use.
“By some estimates, 25–42 percent of uncomplicated UTI infections clear on their own.”
https://www.medicalnewstoday.com/articles/322411#can-you-treat-a-uti-without-antibiotics
I cannot recommend enough Now brand Cranberry Mannose pills for knocking out a UTI.