Can you split the difference?
Box up toys that aren't used in clear bins and label (dolls, toddler stuff, art, old notebooks, etc.)... and stack them in the garage. That way she still "has" them, and can find them easily... but has room for new things. I'd suggest doing it while she's gone and coming in through the garage so you can show her the new "organizing system"... instead of keeping it secret.
For myself I'm quasi-eidetic. I can look at a My Little Pony from when I was 5 and distinctly remember the 40 some odd "great adventures" that go along with said pony. Including a few minutes prior and post. ALL my stuff has memories attached to it. I can't recall them without a prop, but with the prop, I get it all back. From the feel of the carpet under my knees... to my mum cooking dinner to the purple brush in my hand to my sister hanging upside down off the bed making "Is this annoying?" sounds. It's physically painful for me to "get rid" of things... but anything I "store" may as well read "abandoned". But I can't throw them out (I cry, it's really really really hard).,, so I box things up neatly and store them for perpetuity. My own mum is kind of the same. Irritated my father no end (boxes of barbies and hotwheels and odds and ends) until my son, their first grandson, was born and OUT all those toys came. They didn't have to spend a dime on new toys, because all of the boxed ones were "new" again.
Of course, she may well be able to donate sterile looking boxes of stuff marked "toddler toys" later on... but for now... it gets them out of her room and one step closer to "outta here".