Your mother needs to go to a doctor asap if you think she has liquid around her heart or in her lungs. This is a serious situation which needs immediate and fast treatment now and then you can look for alternatives if possible.
My wife has atrial fibrilation and takes warfarin and other drugs daily. Since a few days ago, she started taking nattokinase, fish oil, CoQ10 and vatamin E in addition to her drugs. She tells me that she feels a little better but it's too soon to tell.
That said, i haven't found any official studies about nattokinase, only statements made by people who used it.