Can't give a complete and correct response without a review of the trust. However, is this situation is not covered by the trust terms, sister's share passed to her as of the date of death of mom, subject to administration. Therefore, upon sister's death,her share (and other assets) would pass to her heirs (if no will/trust) or to her beneficiaries.
Answered on Feb 23rd, 2015 at 3:16 PM