That and NASA is a very safety conscious organization. So they want to overestimate everything and include way more than they need. So when she said a couple per day you can round that to 5 for safety, then considering it's a 6 day mission they want to include triple the amount of needed supplies which means 18 days worth. 18*5=90 which is pretty close to 100 so let's round up again. Plus tampons are a useful first aid tool, especially in zero gravity. You shove some into an open wound and it'll prevent blood from spilling all over the very sensitive equipment. Does a woman need 100 tampons for 6 days? Of course not, but she wasn't going to spend a week in the mountains, she was going to space, so the safety precautions were much more stringent