。
She's too young to get married.
Literal
She [topic-は] marry [in-order-to-には] too-young.
The pattern [verb-dict]+には+[adjective]すぎる means 'too [adjective] for the purpose of [verb].' Here には marks 結婚する ('marry') as the goal, and 若すぎる ('too young') reports the verdict on her readiness. Sister patterns: 食べるには量が多すぎる ('too much to eat'), 早起きには寒すぎる ('too cold for an early start'). The auxiliary すぎる ('exceed') is one of Japanese's most productive — attach it to almost any adjective stem or verb stem to get a 'too much / excessively' reading.