I have TT trained 3 kids, to be honest, I never actually 'thought' about which came first. Just went with the flow, if they were ready to TT, we did it, they all also took a while to night train so it all worked out. Two of my kids scaled the cot early so were in a bed well before TT occurred.

We are actually TT this weekend and she has been in her bed with no sides for quite a while, she was one of my climbers.

If you think she is ready for day and night together, you really need to take the side off the cot and stick with it. I wouldn't be putting a side back on in the middle of the night, give it a few nights to start with, you may be surprised just how well she goes