T.G.
I felt the exact same way with my daughter. We put her in a toddler bed because I felt like it was time and she was 18 months also. I quickly found it was way too early for her. She rolled right out of the bed! A good way to try is temporarily putting the mattress on the floor. It will get her used to no rails and if she rolls out it is just simply on the floor. Than you can move up to a larger bed and you can buy those rails that you can buy to go under the matress.. LIFE SAVERS!
hope this helps!