Former ER nurse here, also floated and worked on a palliative unit for a few years. We push IV Ativan ALL THE TIME in ER, and give SC in palliative (only because most palliative patients don’t have/require IV access). The nurse who told you that was grossly misinformed.
You were absolutely right to request IV Ativan for your mother in her last moments, and I’m sure she was honoured to have you by her side advocating for her best interests. Sounds like you did a great job supporting her and ensuring she was comfortable. I’m so sorry you have been second guessing this, stop being so hard on yourself! Don’t ever doubt your instincts!
My condolences on the loss of your Mom?