。
She took a walk with her father this morning.
Literal
She [topic-は] this-morning father [with-と] walk did.
お父さん is the polite, kinship-respectful word for 'father.' Whose father, though, depends on context: お父さん can refer to one's own father in casual speech (especially among family) or to someone else's father in polite address. When speaking about your own father to outsiders, you'd typically use the humble 父 (chichi) instead — a clear example of the uchi/soto (inside/outside) distinction reaching into family vocabulary. 散歩する is a Sino-Japanese suru-verb; the noun 散歩 alone with をする gives 散歩をする, basically synonymous.