Wow, we did almost exactly what Mamazita said.
Around 18 months, we put our kids on a twin mattress on the floor. That way if they did fall, they wouldn't have far to go and probably wouldn't even notice.
When they woke in the middle of the night, they would come straight to our bed and climb in. They never went anywhere else. If they did get out of bed, they usually weren't very awake, just looking for some comfort from Mommy and Daddy.
I can't think of any time that they did anything other than come straight to our bed. Even when our almost 8 year old wakes up before we do, which is rare, he either comes straight to our room to wake one of us up or does this right after he goes to the bathroom.
ETA - I guess I do think you're over thinking this a bit. It's helpful to assume that she's going to be just fine and then deal with any challenges as they come along. She really might be just fine!!!