Sorry for quoting myself, but in this video interview-
Reporter asks Mom, what was the last conversation you had with your daughter.
JS answers - we spoke about her birthday party, she had a birthday party on Sunday. She had a great time, I couldn't make it because I was working. But she had an amazing time, she was so happy with all her gifts - uh, uh, I, I told her good night, um, yeah that was it. I, I wasn't the one who took her school, that was my partner, um, yeah.
So I think it's clear from this exchange, JS did not see Maddie after she went to bed Sunday night. Hence the "last seen" description of her clothing. She didn't see what she went to bed in, only what she wore home from the party, which I assume was the dress we've all seen in the photo. I'm convinced Maddie's room is upstairs, Mom's room is on the first floor of the condo, so this makes sense IMO.