Maybe that will work?

If you are sure she must be in the studio, then put some fresh food out and leave. If she can come out from hiding, she will eventually. She’s scared and needs time to decompress and explore and feel safe. If the food is still there after 24 hours, then I’d do another search to be certain she isn’t stuck in some very tiny hiding spot.

Maybe remove it or at least take her essential items out so she doesn’t have to go in it so eat or use the litter box.
It might remind her of being trapped or caged.

we had a terrible storm. She freaked. I spent 4 hours looking for her, knowing she was in the house -- but where??? I finally found her but it required welding gloves to get her out of hiding whereupon she immediately escaped to hide again. This time I decided to let her be. There was food and water available, she couldn't get outside, and she could find her brother. Another three days passed before she ventured out. Now she comes out and plays all night long. I can get close but having had feral cats I've decided to let her set the time frame. Just be careful she doesn't escape out the door if you leave. Her brother is super friendly so I'm sure she'll eventually take her cues from him.
Have patience.

When I had to move across country, I had everything out of the house but my three cats. Two of my cats were out in the open, but the third, a little six-month-old Calico. I looked behind every door, in every closet including those with closed doors. What the heck? Not in any cabinet. I knew she hadn't escaped because I saw her inside when I last closed the front door. I finally thought to look on the gap side of my fridge. No. Then I tilt walked the fridge out. There she was! Behind the fridge! No way I would have ever thought of looking there if the apartment was still furnished and full. Could she be there? If this happened now, I would reach around to the back of the fridge with a camera to see if she was there.

Having patience and remaining calm are critical. It is not unusual for a cat to hide like that. Move the litter box, food, water, and bed out of the playpen. Keep water and food away from each other. Establish a routine, a ritual. Fresh water, fresh food regularly. Talk quietly and move slowly while you are doing this so he/she gets used to your presence and associates you with predictable dependable behavior, and with food and water. Let her/him engage you at their own pace. Was the kitten from a shelter? Are you offering the same food that he/she got there?

results. You’d never guess now that she was ever feral. Biggest love sponge kitty I’ve ever known. Patience is key, but they all tame at a different pace. Wish it were easier to make them understand that we love them and won’t hurt them. Good luck

I'm supposed to bring her in for a checkup for her URI tomorrow (Wednesday). I left the playpen door open and she did come out last night and use the litter box and eat, so I know she's there, but when I went down this morning there was no sight of her. There's a bunch of musical equipment belonging to my husband shoved in one half of the studio and that's where I think she is, but I can't get back there at all. I don't know how I'm going to get her to the clinic tomorrow. Also, husband doesn't know she''s there. I had a foster the whole week last week and he didn't know it either.