My response is Yes do it without her.
I'm just completing the Simplicity Parenting Group Leader's training and all the parents who have embarked on the decluttering have this big thought (oh no my DD or DS will be upset) in fact the opposite is true. There's a huge amount of experience of this decluttering out there and no one reports a child getting upset. As long as you know the treasured items and don't chuck those...
You could ask her what her five favourite cuddle toys are (and end up with 10 because she can't decide) but that's far fewer than the 30 you might have lurking in the cupboards, under the bed and in her toy box.
Kim John Payne's simplicity parenting has a great checklist for what's a keeper and what to throw (or recyle /donate to a charity shop / put on ebay).
1. Anything broken, missing a part, needs batteries to work
2. Duplicates (six barbies - really?)
3. Toys Fashioned on TV or Movie characters - point to consider is do you want your child's own open imagination to be active when they play or to have it dampened because they are playing with a Pixar / Disnesy Creative genius who has handed down his or her ideas to your child ?
On that last point I can share my children have created their own book series called the Nomnoms - drawn all the pictures and made up all the characters - it's fantastic and yes they have seen books of characters etc to get some of the ideas they've used, but they also have enough free imagination to create this whole new world.
1. Open imagination - scarfs, pillows, wooden blocks, pens, paints, nature (pine cones, stones, shells)
2. Toys in a toy library - recycle them out every three months.
3. Treasured items - which may well be TV characters :-)
My DD has a bag full of polly pocket sets that she treasured, and five months after my first round of decluttering she announced to me the other day "Mummy I don't want them any more".
Start with one shelf
and then off you go step by step !! Celebrate each draw cleared. Try not to procrastinate. Come back to it next week, next month... post your successes here ! and good luck !