Are you telling us that this gift is discretionary under the terms of the trust, or are you telling us that the trustee would violate the terms of the trust if she were to give you the money? Are there any other beneficiaries, other than you and your sister?
If the trust does not compel the gift, then even if the distribution is authorized by general language it would normally be within the trustee's authority to decline to exercise that discretionary power. It's unlikely that you could compel her to give you the money if she later changes her mind, but that's something that can only be determined based on a review of the documentation. Is there a reason you don't want to ask for the money?Quoting _zardoz_

