The correct answer is D. was regretting that she couldn’t go.
The sentence “She was sorry she didn’t attend her friend’s wedding” indicates that she feels regret about not attending the wedding. The word “regret” means to feel sorrow or disappointment over something that has happened or been done. The phrase “that she couldn’t go” indicates that she was unable to attend the wedding, either because she was not invited or because she was unable to make it for some other reason.
The other options are incorrect because they do not accurately reflect the meaning of the sentence. Option A, “regretted she can’t have gone,” is in the past perfect tense, which is used to talk about something that happened before another event in the past. In this case, the other event is the wedding, which happened in the past. Therefore, the past perfect tense is not appropriate. Option B, “was regretting she does not go,” is in the past progressive tense, which is used to talk about something that was happening at a specific time in the past. In this case, the specific time is the wedding, which happened in the past. Therefore, the past progressive tense is not appropriate. Option C, “will regret she didn’t go,” is in the future tense, which is used to talk about something that will happen in the future. In this case, the future event is the woman regretting not attending the wedding. However, the sentence does not indicate that she will regret not attending the wedding, only that she regrets not attending the wedding. Therefore, the future tense is not appropriate.