Mitch, we put Lindsay and Erin into a big bed when they were nearly 2, but mainly cause we needed the cot for the next one LOL. Paige was 18 months. I found that to stop them rolling out, I put a pillow under the matress to prop it up so they would have to roll up hill to get out. Maybe you could trial her with no side on the cot and see how she goes with that, cause sometimes it isn't just a physical thing, but an emotional one for them too. Be prepared for her to fight you a little once she realises that she can get out