If her hemoglobin level is down to a 4, it's likely to affect her mentally as well as physically. I'd get over there right away, and, outside your mother's presence, make sure those JWs understand that there will be severe consequences for them if they interfere with you in doing what is right for your mother (legal consequences).
Next, I'd ask your mother where in the bible that it says that certain small amounts of blood transfusions are ok, while other larger transfusions are prohibited. The JWs are ok with organ transplants, but not blood transfusions. There is no way to excise all the blood from a transplanted organ; hence, the recipient of an organ transplant is getting a blood transfusion, even if the amount of blood is slight. The JWs are totally inconsistent in their approach to this issue; maybe seeing that will help your mother understand.
You are your mother's best hope for survival. Good luck to you, I wish you and your family the best!