The fact that you sought out the horse forum, registered to post a thread.. makes me believe that you really and truly do want to ride horses despite your fears holding you back.
I think your female friend was just teasing you, seeing as we females have zip idea about how much it can hurt or even what it's like to deal with.. so likely she was trying to keep the situation light and enjoyable.
You will get hurt in horse riding, in multiple ways. But. The more you ride, the more your body learns to adapt, and the less 'mishaps' such as this one.. occur.
The stronger your core, the stronger your riding.
"Strength is the ability to use a muscle without tension"