S.H.
I don't think it's a big mistake to sleep with your kids. I think it is a gift, but that's just me. Soon enough you'll be heartbroken that she's not a big part of your daily life any more and you'll ache to feel her warm little body next to you.
I would be terrified if I were her and in a brand new house and alone in a dark room for the first time without you, and crying because I'm scared and being in the new house means mommy doesn't come when I'm scared. That sounds cruel to me.
Wait for one month after you move in to put her in her big girl bed. Start touting the greatness of a big girl bed and then, two weeks before the day you plan to move her, tell her about the special day and talk to her about it daily in an excited for the big girl voice. Give her a special stuffed animal with special mommy and daddy love inside it. Wear it under your shirt for the day (if you are home) so it will smell like you. Spray a squirt of your favorite perfume on it.
If she cries, go to her. After a c ouple of days you can let her cry it out if you feel that's the right thing, but make sure she feel safe in the new space first.
Moving is really stressful for a small child, who depends on consistancy for security. She's also always had grandma and grandpa around and now they are gone. She'll be missing them and that will weigh on her heart. Taking you away at night in a strange place and making her cry herself to sleep, terrified, doesn't sound like a good plan to me.