Your description of her symptoms and behavior is classic. Her cognitive and emotional state has been negatively influenced by her illness, change of people around her, change of environment, along with all the "procedures" that are being done to her and around her---none of which she able to understand. So, this creates fear and paranoia. Any time she responds to something (anything) with such behavior, the best thing to do is to back off. Reassure her. Let her relax for awhile. Then re-approach later.
Hopefully the hospital staff can complete her treatment as soon as possible so that she can return to more familiar surroundings and routines. This will help a great deal.
The other thing to consider might be the actual importance of the test. Ask yourself if any findings are going to change her treatment plan to improve her life. If not, maybe it really doesn't need to be done. Just a thought.
At this point, the primary goal (I would think) would be her comfort, be that physical, emotional, or cognitively.
Good luck to you. And best wishes for your Mom's recovery.
You're welcome, and thank you.
(note: I must post this as an answer, but do not feel obligated to accept again).