Can I change a grantor type trust to complex?

Mom has an irrevocable trust. I'm the trustee. No where in the trust documentation does it state what type of trust it is (simple, complex, grantor). Last year the accountant filed the trust's first tax return and checked off Grantor and paid no taxes on the 1099-DIV the trust earned. Instead, he put the sum on mom's personal tax return. So the trust paid no taxes. This year I'm doing the filing and I think it should be Complex (no distribution, no K-1) and the trust should pay the tax on the 1099-DIV. Granted, the trust will pay a higher tax rate, but I think its a red flag if the trust files and pays nothing.