She should be able to walk by 2.5. At my old location, in the country, once kids turned 3, they walked 4km every morning during non-snowy months. Surely a 2.5 yr old should be able to get to the school. Yes, a wagon would be helpful, but if that isn't going to work, here's what I did:

We had 'Safety Rules' and made a bit of a game out of them. We talked about the safety rules as we got ready to go to start. Whenever a car was coming, I'd yell 'CAR' and everyone had to move off the road and 'Freeze like a popsicle, snowflake, whatever frozen thing we'd picked for the day. The rule was to strike their pose and their feet couldn't move until the car had passed. When we had to cross, one child was picked for the head of the line and that child was responsible for getting us across safely (of course not really, but they felt like it). I would ask what the first rule was (Look all ways with our eyes) - Do you see any cars? No? What's next? Listen with our ears - Do you hear any cars? No? Great! Will we run as fast as we can? No, good. Will we hop like bunnies? NO? Great! How will we get across? Walking feet! Terrific! Show us how to cross safely.

You get the idea.......anyway, I found the more kids felt it was a game and that they were doing a good job and participating, the more successful it was. It takes some training and time, but once well established, runs like clockwork. Granted, this was in a rural setting. Not sure how fun this would be if there's a lot of traffic