。
Dinner was her own cooking.
Literal
Dinner [topic-は] she-of [honorific-お]-hand-made be-[past-だった].
お手製 ('handmade, homemade, made by one's own hands') is a friendly, complimentary word — often used for praising home cooking, handicrafts, or any personally made item. The お- prefix is honorific; 手製 is 'hand-made' (lit. 'hand-manufacture'). The whole phrase is a warm acknowledgement.