I enjoyed reading your post. I agree with the 3 ethical principles you chose they are the exact same ones I chose. Autonomy, veracity and beneficence were all used in this scenario. The two that we both did not use, that are also equally valid are nonmaleficence and fidelity.
Nonmaleficene is the ethical principle to do no harm. Mrs.Chan’s nurse followed this in supporting Mrs.Chan’s decision to stop further treatments. Surgery, radiation and chemotherapy all harm Mrs.Chan