Omg. I punched my sister in stomach during her periods. ?

Ok she's 24 and I am 19. We do have some fights rarely other something. She was kicking me again and again'. I was really irritated and by mistake gave a light blow on her stomach. She collapse down with pain and ran in her room. Later our mom scolded me like anything. I do feel guilty. she's been in pain since. Also she was holding her stomach like forever'now. What do I do?
Omg. I punched my sister in stomach during her periods. ?
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