Assuming you are a beneficiary of the trust, and the trust is now irrevocable (not a living, revocable trust), any distributions from the trust to you are never a "gift", they are a distribution.

Part or all of the distribution may be taxable income to you. The trustee(s) of the trust can decide whether they are distributing principal or income to you, and in what percentage. This will be reflected in the Form K-1 that the trust will have to issue to you. Any of the trust's income (dividends, interest, capital gains) that are distributed to you as part of the distribution can either be taxable to you, or the trust can retain the tax liability and pay the taxes itself -- this is at the discretion of the trustee(s) (unless the trust document says otherwise).

On the other hand, if it is simply a revocable, living trust, then the fact that it is a trust is basically irrelevant. In that case, it is a gift from your mom to you, and the receiver of a gift never owes taxes. Your mom probably wouldn't owe taxes either, just will need to fill out extra forms at tax time to add it to the "lifetime exclusion".