。
I'm sure she'll come right back.
Literal
She [topic-は] right-away return-come [quotative-と] am-convinced.
~と確信する ('be convinced that / be sure that') is the formal/strong sibling of ~と思う ('think') — used when expressing firm belief rather than tentative opinion. 確信 ('conviction / firm belief') is the noun; 確信する is the verbed form. The polite ~ています form keeps the register appropriate for business, formal-spoken, or careful written contexts. 帰ってくる ('come back') with the inward ~てくる locates the return as moving toward the speaker's location.