Does anybody who gets money from a trust have to file a K-1 with their return?

My wife is the trustee for a trust left by her now-deceased parents. She's been sending small amounts of money to one of her sisters to supplement her social security income. Does the sister need to file a K-1 with her return? The trust will file it's own taxes with a K-1, but does anybody who receives money from the trust need to do the same?