I'll approach this a little differently - describing how I discovered medicine WAS right for me.
I entered college unsure what I wanted to pursue. I explored business, economics, computer science, chemical engineering, and pre-vet. Only after this did I stumble into medicine (in my 3rd year of UG) and find the field that fit me. I think having such breadth of exploration aided in my ultimate decision to pursue medicine. I knew what I was looking for in my career and had points of references of things I liked and didn't like in other fields. No field is perfect. There's pros and cons in everything.
Your goal should be to find the field that balances these in a way that will make you most happy. I will say, I could see myself happy and satisfied in most of the careers I explored. But I felt that medicine would make me the MOST happy. When thinking about your friend, the question isn't whether or not she is happy as a physician, but whether she'd be happier as a computer engineer. You don't want to have regrets.
As far as my pre-med experience, switching late gave me a different perspective. I remember meeting pre-meds my first year and I did not click with many of them. I didn't like the intense focus on academics, as many of those I met seemed to integrate this heavily into their identities. It was stressful being around them - always talking about studying, scores, grades, etc. You can succeed academically without doing this. I preferred my friends from previous majors who were able to detach from the schoolwork and enjoy hobbies and activities away from scholastic endeavors. Certainly there are people in medicine like this, but I think the intense competition and academic requirements does often lead to overly identifying with ones academic self.