Why are people thinking that she is vomiting due to having seen her brother have sex? To me it's quite obvious, especially with the suspicious messages the sister got last chapter: Her husband isn't at home a lot, she had an affair/one-night-stand, regretted it and doesn't want anything to do with the guy, and is pregnant. The stress of the pregnancy + the whole situation was just too much for her, and she needed to vomit