I am sorry for your loss.
Was the trust a revocable trust (i.e., grantor trust) that would have been treated as having been owned by your mother while she was living?
If so, then the trust is treated as a disregarded entity during the time your mother was alive and any income, gain, etc., would be reported on her individual income tax return (1040).
After she passed, the trust would generally become irrevocable and a separate taxable entity with any income, gain, etc., reported on Form 1041.
