Possible Fall from top of cage?

I had a wonderful Fancy Green Cheek Conure. She was 10 months old and have had her about 6 weeks. She had been in two pet stores before we found her. In that time, she has learned to trust us, step up and to mimic my whistles. She responded very quickly to clicker training. We also have an 18 year old Gray Cockatiel that we inherited from my mother that we have had for about 9 months. These birds are my first but I have just fallen in love with them. The Cockatiel Charlie responds very well, is friendly, a bit bitey but loving, talkative and sings. The Conure, Skittles had been very friendly, learning and playing all the time. While Charlie doesn’t play as much, Skittles loves to play, climb, and hang upside down in his cage. They each have their own cage.
While I was out of town last week, my husband uncovered Skittles one morning and found her face down at the bottom of the cage - she had passed during the night. We do cover them both at night and they are usually not active when they are covered. We are very careful with fumes of any kind so I don’t believe that was an issue. Because Skittles had not experienced any signs of sickness we wonder if she fell and broke her neck. Is this possible/common? Did I have the cage setup wrong? I don’t want to get another bird until I know if the cage is ok. I’ve attached some pictures of Skittles and her cage. I did have a soft hut hanging on the side near the bottom as well. The cage is an 18” x 18” x 30“ high cage.
I’m just heart broken. Comments and advice welcome.

Sorry for your loss. You cage looks fine to me.

So sorry you had to go through that. Cage looks ok to me too.

I am truly sorry for your loss. Unfortunately the only way to find out the answers you seek are to have a necropsy carried out by your AV. Again so very sorry.

I am so sorry to hear.. your cage looks fine to me. I really think you should take little Skittles to the AV to figure out what happened. Please do and keep us posted.