Leashes and fences are your friend.
Seriously though. She's a baby, and no matter how good a trainer you are, she's not going to reliably be able to understand or follow all the rules yet, especially one as hard to grasp as "walk on this bit of ground not that bit of ground." By making sure she's never physically able to wander into the road, you're both protecting her and making sure she never develops the unsafe habit of walking into the road. Honestly, as both a dog owner and a driver, I'm not a fan of dogs of any age off-leash on the roadside. Too much can happen. But especially so young, she needs physical boundaries until you've really worked on her understanding and reliability, and until she's mature enough to have better impulse control.
Seriously though. She's a baby, and no matter how good a trainer you are, she's not going to reliably be able to understand or follow all the rules yet, especially one as hard to grasp as "walk on this bit of ground not that bit of ground." By making sure she's never physically able to wander into the road, you're both protecting her and making sure she never develops the unsafe habit of walking into the road. Honestly, as both a dog owner and a driver, I'm not a fan of dogs of any age off-leash on the roadside. Too much can happen. But especially so young, she needs physical boundaries until you've really worked on her understanding and reliability, and until she's mature enough to have better impulse control.