It should be capital gain with a long term holding period depending on facts and circumstances. The details, could mean that the stock might be considered a short term sale to your mother.
Even though the stock was in the trust, it depends on who is considered the owner of the stock. It may mean the ownership was transferred to the trust, in which case the trust should sell the shares and then distribute the money to your mother. You should check with a tax attorney who is an expert in trusts and estates. Also check the documents used to establish the rules of the trust.
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