。
She was tricked into buying worthless stocks.
Literal
She [topic-は] [was-deceived-だまされて] value [genitive-の]-not stocks [object-を] [was-made-to-buy-買わされた].
Two passives stack to mark a double victim. だまされる is the plain passive of だます ('to deceive'). 買わされる is the causative-passive of 買う — built by chaining the causative 買わせる ('make buy') with the passive ~られる, yielding 'was made to buy.' Together: 'deceived' as outer frame, 'made to buy worthless stocks' as the resulting forced action. 価値のない is the no-form ('without X') of nominal predicates: 価値がない → modifier 価値のない. The whole sentence structurally mirrors how Japanese tracks suffering and unwanted obligation through layered passives and causatives — the grammar carries the indignation.