I am sure you know that when her fellow JWs find out that she is having surgery, they will flock around like flies on dung. It can be difficult for her, you and her doctors to have private conversations in a standard hospital room.
Please make arrangements to discuss the blood issue at a time and place where privacy is assured; and while it is easier to have such a meeting with primary care physicians and surgical staff, it is often more difficult to have private conversations with anesthesia. The anesthesiologists often administer blood and blood products. So, discuss ahead of time how a private meeting with anesthesia can be set-up.
Just my humble opinion based on my experience.
Hope it all turns out well for your daughter and for you.