I have two children. My first moved to her own bed around 3, and was sleeping through the night regularly by the age of 4, although I still had to lie with her for a long time. I'm not sure when that stopped, honestly. I know that by the time my second daughter was 3, my older daughter was 7, and the two of them started sleeping together one night. This went on for many years, and then in 2012, right around the time my younger one was turning 9, my older one decided she was done. There was some petty argument where she got thrown out of the bedroom, and she said it wasn't worth it. And now she really hates her sister's room.
I've had a lot of issues with my 9 year old not wanting to sleep alone, but her issue honestly is that she becomes afraid. For months she would regularly wake at night and come in and wake me up to take her back to bed and tuck her in. One night she was so upset I told her she could sleep on the floor next to my bed, so she made up a little pallet on the floor with pillows and blankets, and slept there. She has a double bed, so I could sleep with her, but there was so much stuff on the other side of her bed that it would be difficult, but one night I did sleep with her, and she really liked that and wanted me to sleep there again.
After she turned 9, we took her to a therapist because she seemed to have a lot of anger issues, and was having major meltdowns related to homework. The doctor involved gave her a prescription of Concerta to see if it helped, thinking this could be ADHD, but we also had therapy to deal with her behavior issues. During the time she was taking the Concerta, we didn't notice much of anything changing in relation to her behavior, but her night fears became worse, which I had heard could happen, so we eventually discontinued it. And it seems since then, things have gotten better. She does sleep with her light on all night most nights, unless I can turn it off when I go to bed, but that may wake her up. Sometimes she gets up and turns the bathroom light on too, but she's really cut down on coming to my room. That really hasn't happened for awhile. She isn't supposed to do this, but sometimes she finds ways to sneak electronics into her room so she can entertain herself until she falls asleep, but she needs more sleep than she gets, so we take away her electronics if we notice she's taken them with her, and she loses the use of them for the next day. Our dog sleeps on her bed, so this is always comforting to her.
For awhile it was really bad with her crying about the after-images she was seeing when she closed her eyes, but a lot of this anxiety is gone now. Of course, as a baby, she was the good sleeper. My older daughter was the clingy one who wouldn't sleep through the night.
My only suggestion is to see if there is something more going on with her and not wanting to sleep in her room at night. I was also a very anxious child, and I often slept in the same room with my sisters, but around 12 or 13 I wanted to be alone more often. My daughter knows it's not really possible for her to sleep in my bed at night, but when things are bad, there is the option for her to sleep on our floor. So maybe put strict limits on what she cannot do, but have a little more leeway with what she can do.