。
She tried to make him happy, but it was no use.
Literal
She [topic-は] him [object-を] tried-to-please [but-が] futile was.
Notable for its choice of the older/colloquial ~す causative 喜ばす rather than the modern ~せる form 喜ばせる. Both work; the ~す form survives in fixed expressions and casual speech (済ます, 怒らす, 笑わす), while the textbook ~せる/させる form is the productive default. 喜ばそう is the volitional of 喜ばす, parallel to 喜ばせよう from 喜ばせる. The volitional + とする pattern 喜ばそうとした gives the 'tried to please' reading; the past form often hints the attempt didn't succeed. The clause-final が is the soft 'but' connector, and 無駄だった delivers the verdict.