The very first thing I would do is work with her to go through her entire room - closets and dressers to determine if she has stuff, especially clothing that she no longer needs. After that, I need to actually SEE what needs to be stored, in order to assess the amount of hanging space, folding space, hook space, shelf space needed. So, I would make those piles and see where you are lacking.

Personally, I would do more on the 'purging stuff' end than on the 'purchasing furniture' end.
She will be off to college in two years...

Sure, it's both--take a deep breath and get your boxes and trash bags for save, toss, don't know. My teen always has lots of trash mixed in so just getting that out helps! And usually a lot of clothes and stuff are "yuck" and not being worn. This process is a good part of teaching her how to sort and weed out stuff and not have more than she can manage.

Then, it makes perfect sense to think about logical, useful storage. Doesn't have to be expensive--but as the homeowner, it's actually your call, as you may want to have some say over whether any changes also fit your needs or goals for your home, to install nice closet storage, or choose the quality of shelves, or how hooks are installed, vs. leave it up to the kid. Different things work for different families. But thinking about how best to store things is another good lesson. By all means, set a budget if she is being allowed to "re-decorate" her room, and/or have her purchase some things--whatever is the approach that you use re: finances and such in your family. That is also good training pre-college, unless you want them to think they will have carte blanche at The Container Store!

A number of things can work later for college (I don't mean you should bet on it, since fads and products come and go,but various bins, plastic drawers, storage gizmos that go on closet rods, etc are used in dorms all the time.) So learning to organize "stuff" once it's been pared down somewhat is good training.

Plus, she may be off to college soon, but mine still came back between semesters and apartments and for holidays or whatever and when they do, they have MORE STUFF, and then organizational skills and a functional room come in very handy. If the room has at least decent basics, then it can still get out of control, but be put back under control at invervals! You may be planning to take over her room as soon as she enrolls--some folks do, and that's fine, but if that's not likely, then you are looking at several more years of teen-young adult use of the room.

Does she do her own laundry? I had my DD's doing that from a very early age. I found that helpful in 2 ways--either the girls took better care of their clothes, including not tossing CLEAN stuff in laundry hampers just as the quickest way to straighten up, or regardless, I didn't have to care whether they did or not, since I wasn't doing their laundry.

One thing you can tell her when helping her to purge and get organized and that is, when one thing comes in, one thing has to go out. That's a great habit to get into.

Relax and close the door. I never met a teen who wasn't messy regardless of how much space they have to store things, so don't expect miracles. I think it's a growing up thing. They grow up, want to make a statement but the only thing they have control over is their rooms. The nice thing is that when they have their own place it will be kept like the house they grew up in. My son kept his room like that and his wife--according to her mother--did too. Now their house is kept like her mother and I keep ours.

You could have a closet organizer installed but be sure before you spend the money that it will serve you after she's gone

I have to respectfully disagree with the posters saying all teens are messy....

Personally, I was a complete slob as a child, and although I enjoyed when my room was clean it was miserable getting me to do it. When I was about 13 and away at camp, my parents redid my room with new wallpaper & carpeting, and I loved it. (It was the 80's, and the entire room was pink, grey, and white....) I kept that room clean and organized until I moved out. I think I just needed a fresh start and a place that was "worth it" to me.

When you're overwhelmed by organizing just one room, I have found a combination of the laundry basket & Fedex method works best for me.

Before starting, invest is several large cheap laundry baskets, and if there's no floor space, line them up in the hallway outside the bedroom. Put signs (important! it makes you surprisingly faster) in front of them saying:

Dirty clothing
Clean clothing to put away
Shoes & bags
Books/music to put away
Things to donate
Trash
Things that belong somewhere else in the house

You'll probably need to change and/or add a basket or two, to do whatever seems to work for your daughter.

Then, get things from off of her bed, desk, floor, etc, and toss them in the appropriate basket. Do NOT address what's in a basket at this point. Especially do not make 10 trips to the laundry, kitchen, etc. It's inefficient and a time waster!

Once you have most of the clutter sorted into baskets, you can more easily assess your storage needs. Now is the time to get rid of what you can! You'll already be feeling better because there will be clear floor, surface area on top of dressers, etc.

Now that you both have an idea of what you need to store, take your daughter shopping for organizers. Let her pick, but encourage modularity. In other words, containers that stack, nest, and can be rearranged sometimes cost a bit more up front, but you can make them work for you for years & they're less frustrating.

Hope that helps a bit, and good luck!

I just think this is so telling:

I was in her room this morning, trying to assess and realize that she has completely inadequate storage for her clothing, purses, sports bags, etc.

People forget that the FIRST clause in that adage is the most important:

A place for everything, and everything in its place.

Infrastructure is crucial. It makes organizing possible.

And as for "she's off to college soon"--well, when ARE you going to offer her training and the practice for organizing her life? Now's the time.

So, of course purge.
And of course assess, categorize, and evaluate.

Then, think a bit outside the box. I think the biggest problem, esp w/ kids, is that the stuff they use MOST is often not stored in the most accessible place. And some storage is counter-intuitive (heavy backpacks should not hang on hook; kids toss them int he corner for a REASON.

As you are assessing, look also at where stuff ends up NOW (so, take a good look before you clean up). Work WITH those existing patterns; just provide ways to store things more tidily, with less "spreading."

And definitely, pick your storage solutions AFTER you've thought about what would work. Narrowly spaced shelves (a form of cubbyholes) might work for purses; drawers might work for other stuff. Be a little imaginative.