I went to Grady (now Midtown) HS, and we had plenty of kids who used MARTA, either hoping on a bus, or walking up to Midtown station. I don't know how their experiences were, but it was common enough to be noticeable. I biked, and walked, (and drove when I had my license), and didn't have any issues.

When in middle school, I used a bus and bike to get to after-school martial arts for a while, and also don't remember having any issues there.

So, I'll suggest considering the transit+bike option if that's available, since it allows a bit more flexibility, for example if the bus is missed.

As others have said, MARTA has their 'Say and See' app. There are also help buttons at the ends of each train car, and in stations. I've seen a few people suggest getting pepper spray, which is up to y'all, but you could also look at personal alarms (here are examples which are also rather common to have available if needed while walking / taking transit.