You might try asking if there is another medicine she could take along with the morphine, to address the paranoia and stubbornness.
My husband is on hospice for a brain tumor. He had big problems with paranoia, and during this time (usually afternoon and evenings) he would oppose anything anybody wanted him to do, like take medicine.
He was put on Ativan and Seroquel. I think though that it is the Ativan which causes him to be much more reasonable, and paranoia is just a minor issue now. Morphine is quick acting but does not stay in the system as long. I would ask about something that would keep her more calm, and she might then take the morphine when offered.