You need to talk to a divorce attorney, fast.
Generally speaking, your non-working spouse is entitled to support and half of all marital assets (things purchased or saved during the marriage), however, in your case you could possibly have an advantage in a divorce due to her behavior.
With regard to a tax refund, the assumption is that it is marital property, so generally it is split. If you paid the landlord and for the kids' needs with her share, I doubt you would get much problem from a divorce judge.
Get an attorney, NOW.
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It would be considered marital property and therefore to be "equitably divided" like everything else. I'm not sure how she demands it is all hers. If you use it for marital debt arguably that would be acceptable as well. I would talk with an attorney.