If they were really only gone 10 minutes, not much COULD have happened, I'd think.
Tell her that this is an important issue not only for her but for everyone concerned. She simply MUST tell someone what her feelings are and why -- ESPECIALLY if he did something that he told her NOT to tell.
Ask her who she'd feel comfortable talking with about it and that no matter how 'bad' it is (whatever happened), her mother needs to KNOW what it is so that she can keep it from happening again.
It very well could be the shaved head. My husband shaved his beard when our youngest daughter was about 3, and she ran into the house telling us some story and as soon as she saw him, she stopped in her tracks -- and mid-sentence -- and just stared at him open-mouthed. It traumatized her somewhat. 6 months later when his beard grew back, she put her hands on his jaws and said, "Remember when you were 'bald' down here?"