。
She's usually home on Sundays.
Literal
She [topic-は] usually Sunday [topic-は] home [at-に] is.
Two は's stack here: the outer 彼女は sets the topic of the whole sentence ('as for her'), and the inner 日曜日は contrasts the day in question ('on Sundays specifically, as opposed to other days'). This contrastive layering is one of Japanese's most characteristic syntactic features — multiple は's mark differently scoped topics. 家にいる ('be at home') uses the existence verb いる for animate beings (vs ある for inanimates), with に marking the location. たいてい frames it as the typical weekend pattern. A short, clean sentence with rich structural detail.