A quick update: Sweet Pea went to bed last night in her big girl bed without any issues and around 3:45 I heard a thud and then a few more thuds. I went in to her room to find her sound asleep on the floor with her seahorse not far from her head. She had thrown her seahorse and probably went out after it, but fell right back asleep. I picked her up and moved her back into her bed and she didn't flinch.
At 6am we started hearing her again. I was clearly not fully awake because I thought she was talking and playing in her room with the mirror closet doors. Daddy was much more awake and informed me that she was in the living room playing with her new cookie jar toy that speaks quite loudly. He was kind enough to get up and let me sleep for a while more.
I picked up a baby gate from my sister's house this morning and we will be putting it at her door so she can't get out of the room without us letting her out. Having her wander the house is a scary idea! Let's hope tonight goes just as smoothly as last night!
Update: Sweet Pea went to bed again tonight smoothly! Keeping our fingers crossed it continues through the night!