This isn't your trust, and the trust lawyer works for your mother and father, so if they don't consent to you getting a copy of this document, then you won't get one. It sounds like your interest is angering your mother, and she clearly doesn't want to have this document, so maybe you should resign yourself to not being so interested.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Ms. Koslyn is right. The trust belongs to your parents. If one of them says "no", then the lawyer cannot give a copy to you. On the other hand, if your father tells the lawyer in writing that HE wants a copy of the trust, the lawyer should send it to him (after all, your father is his client) ... and if your father wants to give you a copy, he certainly can.
But Ms. Koslyn is correct that you risk angering your mother ... and she probably has the right to change at least some of the trust. So even if you persuade your father to give you a copy of the trust, it just might anger your mother enough that she leaves no portion of her share of the estate to you.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.
The attorney represents both your mother and father, and if one of them doesn't want to release a copy to you, the attorney can't do so. Your father can give you a copy, or get one for himself and give it to you.
It's a difficult situation for you, as your mother can make good on her threat and disinherit you, as she has no obligation to leave you anything from her part of the estate.