Answer: Her fearful reaction is a response to the relation she makes between the painful process and alcohol.
Explanation: it is normal that humans get to relate something specific to a negative experience. In her case, the feeling she had to experience, the painful endurance she had to go through, as a way to be cured from rabies, makes inevitable to find a rejection to be matched with, in this case, alcohol, which triggers her fear. This issue can be related to the Classical Conditioning, which is related to the connection between a stimulus and a further response to it, which is Natascha's case.