。
She made a strong case for the importance of education.
Literal
She [topic-は] education [genitive-の] importance [object-を] forcefully-argued.
力説する is a vivid Sino-Japanese verb: 力 ('force, strength') + 説 ('argue, expound') = 'argue with force, emphasize strongly.' Heavier than 強調する ('to emphasize') — implies passionate or impassioned argument, not just stress on a point. 重要性 ('importance') uses the suffix ~性 to nominalize an adjective into an abstract quality: 可能性 ('possibility'), 必要性 ('necessity'), 国際性 ('internationalness'). The whole sentence reads like a journalistic summary of an op-ed or speech.