What an interesting problem. I'm so sorry you've been through this exasperating experience.
Two thoughts occur to me, J.. This new anxiety is appearing during the time your daughter would still be processing the theft, and observing and processing her parents' emotions in the wake of that event, too. You note that she's pretty observant, and emotionally, that's true of most kids. Sounds like she'd pick up not only the emotion, but probably much of the content of what she's heard from you and Dad, whatever you discuss within her hearing.
And emotionally, with your family's experience of being invaded and suffering a loss, this particular loss was very personal to you, and actually represented your daughter and her little sister. Emotionally, that might be processed similarly to a personal harm, or at least the threat of harm. And yet, these were things, and so she may be worried for the material objects in your home, as well.
In case any of that is valid, and there are good reasons why it may be, I'd do three things. Change the way you talk (and think, if possible) so you don't feel like "the victim." It sounds like that would be one way for your daughter to internalize the theft. I want to tell you, I have had artwork stolen from shows and galleries, and it's lost time, energy, materials, financial value, and beloved inspiration. So I probably know what you're feeling about "those a-holes," and it won't help you or your daugther.
What she needs to start hearing from you is that you enjoyed the process of making those figures, you were happy to think of them as "daughter-art," but they were still things, not the real children. You're sad that they're gone, but you'll have just as much fun making another set, and maybe they'll turn out even better. Think of what you'll all learn! And whoever stole them must have admired them. It's too bad that some people haven't learned right behavior. Next time, you'll (put the snowgirls in the private back garden/chain them down/some other solution).
So yes, that's the most emotionally healthy alternative: remake them and tell her that sometimes, people do bad things, but we can persevere. Not even persevere – we will thrive. And be glad we have our needs met so we can spare some of it for the world, even if that wasn't our original intention.
In other words, reframe the event, both in your mind and in your words and behavior. Injustices and challenges come to all of us, not always deserved. They just are. And still, the best life is to sustain as much simple contentment as our strength allows. Even if sometimes we have to sort of make it up as we go.
The other thing I would do is to acknowledge your daughter's anxiety, not try to reason it away, and help her find the resources in herself to deal with this and move onward and upward.
There's a really wonderful book that teaches parents how to empathize with kids in a way they can hear and take in, and give them a safe space to spill what they've been working through, and where they might have gotten stuck. Beg, borrow or buy a copy of How to Talk So Kids Will Listen, and Listen So Kids Will Talk, by Faber and Mazlish, and try their clear, understandable techniques. Kids cannot be talked out of fear or anxiety. Nor can most adults. But they can learn how to examine and reassess a situation and see it in a more whole light.
Finally, if all this does not help your daughter overcome her sense of anxiety, a counselor who specializes in children would probably be the next best step. I wish you well, and happy snowgirl makings.
