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Yes, you are correct.  Marriage imparts ownership (you are considered to also have owned the home) but marriage does not impart residency.  So she can claim an exclusion of up to $250,000.  

Then, if you sell your house (the house you owned formerly), you would also be entitled to an exclusion of $250,000.  To qualify for an exclusion of $500,000, you would have to wait until at least March 2028, because your wife can only use her exclusion once every 2 years.