The sentence is grammatically correct.
Student or Learner
Read the sentence: "While talking, she draws something on the wall with the blood-stained finger."
Is this correct?
P.S. The blood did not come from her finger. The blood was not taken from her body. Is the blood of an animal!
A better title would have been The blood-stained finger.
'Thread titles should include all or part of the word/phrase being discussed.'
I would write "her" finger, not "the" finger unless it was an amputated digit.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
If you use the, she only had blood on one finger. I would use her too.
I would use "her" or "a/one".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.