Oh, dear! I hope you find her!

I personally would go very slowly through the entire apartment, closing every door, and looking room by room. If you can move as much as possible to the center of the room or at least all in one spot, it might help. Try any box with an opening she can squeeze herself into. Go slow and quiet. Think like her. Warm, cozy, dark spots. There was a thread a couple days ago where the owner found their snake in the top of the closet under some paperwork. They're sly little devils!