If Jean Smith (see below) dies AFTER the surviving Trustor dies, how is her gift amount distributed? She has several adult children]

I cannot be sure how to interpret a trust based on one clause, but this clause says that if Jean Smith is alive when her sister (the surviving Trustor) dies, then the trust should pay Jean Smith $10,000.  If the $10,000 is not paid to Jean Smith before Jean she dies, then the trust should pay her estate, unless there is specific language in the trust stating that failure to pay someone while they are living results in a lapse of the gift.  But, in general, a trustee's failure to make a payment required by the terms of the trust should not cause the gift to lapse.