。
She hasn't been entered into her husband's family register yet.
Literal
[topic-は] still husband [genitive-の] family-register [into-に] has-not-entered.
戸籍 (koseki) is the Japanese family register — a uniquely centralized system tracking households (not individuals) through births, marriages, divorces, and deaths. When two people marry in Japan, one of them (legally either spouse, but historically the wife) leaves their parents' koseki and is added to the other's, creating a new household entry. 戸籍に入る ('enter the family register') is the formal way to describe legally joining a household by marriage. The sentence implies a marriage that hasn't yet been formally registered — perhaps a couple living together but not yet legally married, or a paperwork delay after the wedding ceremony.