What you're looking for, unfortunately, doesn't exist (at least from my knowledge). I'm aware of being able to input/output internet connections out of HDMI but I'm not aware of any type of adapter to let you pass USB out of it. VGA would also not be possible as this is a type of video-output.
Okay, so are there ANY other options than using a USB port? I really don't want to buy her a new laptop just because she can't use her mouse.