、。
She's the head of the sales team, so her only superior is the sales department manager.
Literal
She [topic-は] sales-team [genitive-の] head is [because-ので], superior [topic-は] sales-department-head only is.
Japanese workplace organization runs through a clear hierarchy of titles: 部長 (department head) > 課長 (section chief) > 係長 (subsection chief) > 班長 (team leader). 班 ('squad/team') is smaller than 課, so a 班の長 ('team head') sits low on this ladder, directly reporting to a 部長. 営業 ('sales') describes the division's function. ~なので ('because, given that') is the noun-attaching form of the explanatory ~ので — slightly softer than ~から, presenting the reason as objective context rather than personal justification. だけ ('only') restricts the topic.