It's highly likely she doesn't know why she's feeling anxious. My guess is, it's related to a physical level of anxiety - from adrenaline - and she doesn't know the cause. No one with anxiety knows why they are anxious, they just are, and then they seek ways to reduce that level of uncomfortable anxiety. For her, it's seeking closeness to her mother at night.
A good compromise would be to tell her she has to at least start in her room, at a reasonable time (before 10 maybe?) and if she wakes up in the middle of the night and wants to come to your room, there's a sleeping bag with a pillow on the floor for her. She's welcome to use it if she needs to.
I think she would benefit from counseling. Not directed at ferreting out a "why", but to teach her to cope with anxiety better than just giving in to it.
I agree with rockrose. She could just be an anxious child. She's now 10, school gets more demanding, social situations are more demanding, parents are more demanding. I have a very anxious son. there can be no reason that I can personally come up with for why he's wringing his hands and fretting or telling me he's scared and yet he is. This is organic for him, within his own genetic make up that he is prone to general feelings of anxiety.
Agree that helping her with coping skills is essential.
Also, since this spurred up in the past 4 weeks and includes day time difficulties in mood, I'd consider that something is going on that she isn't telling you along with the general anxiety feelings.
Try to stay patient. She feels bad inside already and really can't help how she is feeling and reacting to the feelings. Make it a process of easing her back out of your room (and sometimes enticement of rewards and positive reinforcement can help). good luck
I agree with all above. If this just started happening 4 weeks ago - something is going on. And she is not able to express it - makes sense at her age.
There are some books aimed at her age group that could help. For example, there is "Don't Rant and Rave on Wednesdays" "In this book, Dr. Moser explains the causes of anger and offers methods that can help children reduce the amount of anger they feel. He also gives effective techniques to help young people control their behavior, even when they are angry."
At the bottom of this link, it lists the other books in this emotional impact series. http://www.amazon.com/Dont-Rant-Rave-Wednesdays-Anger-Control/dp/0933849540/ref=pd_sim_b_1
Make sure you read the reviews at the bottom of the link as you get a good feeling for how this series can help.
There is also What to Do When You Dread Your Bed: A Kid's Guide to Overcoming Problems With Sleep (What to Do Guides for Kids). That can be found here.
These will help. Don't be afraid to try them