She has had the best medical facilities available (1)/ but she will not be cured (2)/ unless she does not have a strong desire to live. (3)/ No error (4)

Answer

3

Explanation

Here, unless should be followed by Positive Sentence i.e. unless she does have/ unless she has a strong desire to live is the right usage. Unless is used to say that something can only happen or be true in a particular situation.