piglet oh, then you know your own answer. You think it feels right, you are more relaxed, DD is sleeping almost immediately, and the idea of her going back to her own room is making you fret. So, do it. And, let your mum try to persuade you, but remind her that ultimately, your need to sleep and be assured that DD is safe is the most important thing over and above co-parenting with her. Just reassure her that you value her advice and involvement and doing things together, but when times come that you disagree, your choice has to be the one that comes out on top.
I hope she is understanding and lets you do this without too much fuss.
I personally would have DS back in with us like a shot, if it were not for DH being adverse to the idea, although even he has on occasions wondered if we should just bring his bed back in with us, we all sleep so much better when he is not apart from us. Unlike DD who used to happily sleep in her own room better than with us.
In fact, if DH were even slightly up for it, I would move both children back in with us. I love having them near me.