i dont know when it becomes a "problem", but i feel like there were times in my life that i struggled with this exact same issue! LOL. i was a highly organized child living with a cluttered mom and a very messy sister. LOL
i suppose when it interferes with life in general, or when it bothers her or frustrates her that she "has" to do this. right now it sounds like something she LIKES to do which is different from something she cant help doing.
you can talk to her doctor, but it sounds like its not a problem right now. maybe the going to sleep is an issue.
what you can do to help her is to make her room extremely easy to "organize" with baskets, shelves, bins, whatever she would like. you dont have to buy them, they are not hard to make if anyone in your house is crafty or likes messing with building things (your husband? have a son? or even a neighbor?) that way she could paint and decorate them herself. also, make sure that she will have the time at night to put her things away so she can set her mind at ease.
its not always possible to have everything organized every night, so teach her ways to relax and refocus that thinking into something she can relax with. she sounds like a mom!! one that was really helpful for ME, is to tense up my whole body for a minute or so, squeezing every muscle tight like a fist! then let go, and focus, literally whispering to myself to relax each body part starting at your toes. relax your toes, relax your feet, letting go of a deep breath for each relax. it refocuses my mind on relaxing, instead of thinking about cleaning. typically, i never make it to my head because i fall asleep.
heres a few more things to consider. like i said, my mom and my sister were both messy. are you among the more cluttered types? im not saying that this CONTRIBUTES to her organization, but you can use that to your advantage. if she wants to organize something, perhaps she can help you to clear off one surface in the house. you might thing its a horrible project, but she just might enjoy spending that time with you and it might be something you can share with her and talk with her while doing it. my mom still "brags" to this day that i could take one day and clean the whole house. she literally can not do it. LOL. she tries, but its just not a part of who she is. it is a part of who i am, and im glad to be able to help my mom out that way. its important you do this with her because otherwise she will put things where you cant find them LOL
anyway, i dont think its a problem, but find ways to help her relax when she cant organize everything. ;)