Setting:(not that it matters for the question) Future Earth; there's a colony on the moon and space travel to and from is pretty common though humans are just now getting to Mars.
Problem: My character is a bio-engineered human woman in her late teen years (18 or therabouts) who is normal in every respect except for the fact that she can turn invisible. Unfortunately, she's also petite and is a target for her very large, very mean stepbrother who likes to kick her around. My question is this: what kind of physical reactions come with being punched in the stomach? Obviously pain is one, probably bruising and tenderness for a few days after, but is there anything else? Would she vomit if hit in the right spot? Would there be any internal organ damage if she was hit repeatedly or kicked repeatedly?
Thanks for your help!