。
She has a lot of work she has to do.
Literal
She [topic-は] [a-lot must do-たくさんしなければならない] work [subject-が] exists.
The adjective clause たくさんしなければならない ('must do a lot of') modifies the noun 仕事 — a relative clause cleanly slotted before its head. The internal structure is itself an obligation pattern: しなければならない ('must do'), here intensified by the adverb たくさん ('a lot'). Japanese can stack a quantifier inside a relative clause this way, treating the entire 'a-lot-must-do' bundle as a property of the work. The matrix verb がある ('there is/exists') pairs naturally with 仕事 to give the standard 'have work to do' frame: 仕事がある = 'there is work / I have work.' A neat showcase of how relative clauses pile description before their head noun.