This is one of those times in life when you have to show your daughter how to stand up for herself by standing up for yourself. Get into practice now, because thing like this keep happening in life until you learn to be forceful. If you're like me, you hate confrontation and are very polite, only to be taken advantage of. Like me until a few years ago that is, when I decided to be be audacious enough to stick up for myself. Now I love to have the opportunity to put people in their place when it's justified.
Call her on the phone and say, "Hey, hi, I'm coming over to gather any toys you have there which are my daughter's, what is a good time for you? I've seen the such and such and so and so we bought at Target...(wherever-specify so she can't say, 'nothing here is yours..') and I'll just scoop up whatever else while we're there. Are you busy right now?"
If you think this person (who seems pretty horrid already) is weird enough to run around and hide stuff before you come, you can just show up at the door and do it with the statement (not apology) that you guys need all her stuff together. So what if she ends up feeling like you're at fault somehow. You aren't. And the feelings of someone as rude as she is really shouldn't phase you. You'll feel better, believe me, take a deep breath and go for it!
I want to add, she's being a bully. Show her you are not scared of her. Other things could happen down the road as neighbors if she thinks they can get away with something as ridiculous as taking your stuff. If you go take the stuff and fight a little bit in the process as she tries to keep it, she'll feel like you're stealing from her...which is good. Get on her level so you aren't the victim. You're only taking what's yours.