The credit of your dear ma-in-law was not frozen, unless she dropped her lone credit card in the yard before an ice storm. The actual "freezing" of credit, at least in the most common usage of the term, is typically self-imposed after a person suspects he or she may have been a victim of identity theft. People then "freeze," or lock access to, their credit files at consumer credit bureaus to guard against thieves opening new accounts or otherwise obtaining credit using their names.
What your hubby's mom likely meant was that her credit score has dropped in the short term -- perhaps as much as 100 points -- and that it will stay down temporarily until she establishes a record of paying her mortgage obligation on time. In that case, she can expect her score to begin creeping back up anywhere from six months to a year or so, unless she starts running up her credit cards, making late payments on other debt, or incurring collection arrearages or tax liens.
In fact, a mortgage that is honored to the letter is one of the best things a person can have on the credit report. It typically results in a higher credit score than before the home was purchased. That higher score might be slower arriving if she makes other new major purchases such as a car or a houseful of new appliances, even if all her payments are on time. Such purchases would push her debt-to-income ratio higher, which is a key factor in determining credit scores.
In the latter case, she may have trouble getting a loan to make repairs or improvements to the house, at least in the near term, a scenario she may well consider as having her credit "frozen." A high volume of credit inquiries from lenders in a short period can also temporarily nick a credit score as well.
But if your husband's mom keeps her payments current on everything and doesn't overextend herself, she can start looking for a thaw in her "freeze" sometime around spring, appropriately.
I wish you both good luck!
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