[@Silver Fox]It's more like a potion gets rid of cuts and holes, but it does not recover everything. 

Sorta like an anti-biotic kills an infection, but does not just automatically recover what is taken from the infection. 

So even if the potion closes, based on what was read is that she would indeed need that blood back so her body can function correctly. Of course the body would eventually filter that blood out.

(Note, blood somewhat dies itself the moment it touches oxygen. Blood is normally blue because it does not normally hit oxygen.)  

Again- a potion would seal- but- if her body is struggling to just stay alive, it would not work without the blood flowing decently. 

So right now it is better to just filter it in her body, then close it up. The body is truly an interesting natural machine.