The correct answer is C. didn’t eat.
The sentence is in the past tense, so we need to use a past tense verb. The other options are not in the past tense.
A. haven’t eaten is in the present perfect tense. This tense is used to talk about things that have happened up to the present moment. In this case, it doesn’t make sense to talk about things that Sue has eaten up to the present moment, because we are only interested in what she ate at a specific time in the past.
B. wasn’t eating is in the past progressive tense. This tense is used to talk about things that were happening at a specific time in the past. In this case, it doesn’t make sense to talk about things that Sue was eating at a specific time in the past, because we are only interested in whether or not she ate anything.
D. don’t eat is in the present tense. This tense is used to talk about things that happen regularly or habitually. In this case, it doesn’t make sense to talk about things that Sue doesn’t eat regularly or habitually, because we are only interested in what she ate at a specific time in the past.