Dear Mark, Getting a blood transfusion wouldn't save your mother now. So don't worry on that score. It might prolong her life, but it woudn't cure her. She is going to die happy in the belief that she's been faithful to her God. That's VERY important to her.
However it's important that you get to share some private time with your mother. You can explain this to the Witnesses and ask them to BUTT out for a few hours (though you better put it nicely for your mothers sake). Tell them you have no intention of fighting the blood issue and that you want some private time with just you and your mother. No decent person would refuse you that. If they decline, tell them you are going immediately to telephone the newspapers to do a story about how unreasonable and inhumane Jehovah's Witnesses are. I know this works, coz I was never allowed to see my elderly JW parents until I threatened (in a yelling fit) to take their behavior to the newspapers. They backed off big time after that.
Anyway, if they don't give you the time you request, you have the right to ask the hospital to stop all visitors but family. Hospitals will do that on request from family members, at least they do in Australia. Just stop them until you have spent the time you need with her, then let them back in. Basically Jehovah's Witnesses have nothing better to do, but poke their noses in other people's business and this is why they are intruding into your most difficult hours.
I have to face this sometime in the future too, because my mother has invasive breast cancer and I'm a disfellowshipped Jehovah's Witness. Pls let us know how you get on. My heart goes out to you.
Marilyn