。
She's a better leader than him.
Literal
She [topic-は] him [even-than-よりも] excellent leader is.
よりも is より + も, intensifying the comparison ('even more than, more than ever'). 優れた is the past form of 優れる ('excel, surpass') used as a prenominal modifier — Japanese often uses past-tense verbs adjectivally to mean 'has the property of having done X.' 優れた指導者 = 'a leader who excels' = 'an excellent leader.' Note 指導者 ('leader') is a Sino-Japanese 漢語 compound — formal compared to native words like リーダー (loanword) or 親分 (boss).