although 8 seems like an age where kids should be responsible enough to clean their room - in some kids it just isn't. The skills to organize and be motivated to clean up isn't always there at this age yet.
I'm not sure how you have showed her how to clean or if you have even done this in the past...but sometimes it takes a while to understand and learn the concept of organization. She may be a slower than normal learner when it comes to this and her actions are really showing you that she doesn't really "know" how to organize properly. Sometimes it's hard to understand how something so easy, would be hard for a child...but it can.
When teaching my older daughters and also my soon to be 8 year old daughter, I took the time to help them everytime they cleaned their room. I don't mean doing it for them while they watched..but helping them.
There are always two scenarios...1) their room is so out of hand, the thought for a young child to even begin to sort all that out and organize is such a HUGE task and they don't know where to begin. (This is a touch situation for even a seasoned adult to tackle, let alone a young child). In this instance- I DO actively engage in helping. But we talk it out together while we are cleaning. We take an area and start organizing. all the miscellaneous things get put in a pile in the middle of the room. Once the edges are cleaned we start in the pile and one by one, put those things where they belong. Before you know it the room is clean and they feel that they accomplished something...and the help in this situation is greatly appreciated, and you also helped them mentally learn how to organize things.
Scenario #2- The room is relatively clean, but a few things have come out of organization including clothing not put away. I have found this to work wonderfully in my house. I would give them SPECIFIC little tasks to accomplish. For instance if there are barbies laying out, I would tell my daughter- "Find all your barbies and put them in the middle toy box where they belong". (notice that I specifically remind her where they belong) I walk away and do something else. She would do it and then ask.."Now what?" as I pass her door. Then I would look around and notice some other things out of place and say for example- "Ok, good job, now pick up your books that are on the floor and place them nicely on your book shelf" She would then accomplish the smaller task and then ask again what needs to be done. I know it sounds a bit time consuming to do it this way, but if it is done in SMALL increments it is a LOT easier for a younger child to finish a small task, than a larger task. It is also a way that you are "helping" without physically helping on a DAILY basis! This should be done every night to keep her room organized, so hopefully it won't get to option #1 that would require a lot of your help.
Another thing is rewards. Kids that age like rewards. They probably won't respond as well to taking more drastic measures like removing the clothing away as to getting rewards for taking care of them. Sticker chart with a special treat at the end of each week is a good way to have her keep up her room each day. Also give her another responsibiliy around the house. My almost 8 year old daughter has standing chores that are age specific. I think it helps her find her place in the house and makes her realize she is an important part of the "runnings" of our household.
She dusts (because she likes to spray the windex), she organizes the shoes that pile up by the door, she sets the table each night, and she also is in charge of the walls. She likes to get a clorox wipe and wipe down finger prints or any dirt that gets on the walls or doorways. This is all besides keeping her room in decent array. She also helps her older sisters fold and organize the laundry.
Now,my older girls (11 and 12) have standing chores of either dishes and cleaning up after dinner, or washing,folding and putting away the families' laundry. All three are always in charge of picking up their junk that gets strewn about the house every day also.
I personally think it's never to early to have kids help in the house with some age specific chores. My 11 and 12 year olds could keep an entire house clean. Even though they have standing chores of kitchen/dishes and laundry, they also vacuum , mop, wipe down bathrooms, and dust from time to time as well. (when helping me out on a large scale)
I am proud of the fact that my kids know how to do things and have the skills to take care of a house. I know way to many adults that barely know how to turn on a washing machine or how to wash dishes by hand. That is just crazy!
Sorry I got off track....to sum it all up, I think she is still a bit to young to take on a task that large without more POSITIVE (no yelling) help on your part. Even if you have done the whole organization thing a month ago, you need to help her in small steps on a DAILY basis to keep things going. She'll pick up on it and learn and before you know it, she will be cleaning the house.
Ohh...BTW- I don't give allowance to my kids. I tell them that we all live in this house, and these "chores" are just a part of living in this house. I buy them their clothes and pay for the extra's like the cell phone etc. Those are the perks they get for being a contributing part of the household. If they stop doing chores or keeping up their room, I'm not so easily swayed to purchase things they ask for...and they know why right away - They aren't contributing to the household.
Hope it helps - stay positive and don't give into yelling so soon. Your job is to teach her- not just expect her to know how to do things like an adult.