Maybe she was like "thank goodness he died"
you know probably the regret feelings if they're really have a thing for each other but didn't get a chance to be together because he's dead. But probably the answer is no because he doesn't want her to have any regrets. Just like how she imagine both of them together :( ( sorry for bad grammar hehe)
She felt guilty about his death because if she had let him answer before winter break (and he said yes), they could've spent winter break together and prevented his death. But since he said he didn't have feelings for her, even if she had let him answer before winter break, there wasn't anything she could've done to prevent his death since they wouldn't have spent the break together. Basically, she's glad he didn't like her so that she won't feel guilty about his death. Hope that makes sense (๑>◡<๑)
Why was she glad that he didn’t have feelings for her