。
She's wearing a brooch.
Literal
She [topic-は] brooch [object-を] is-wearing.
つける ('attach, put on') is the wearing verb of choice for accessories that pin or clip — brooches, badges, watches, ties. Japanese famously distinguishes wearing verbs by where the item goes: 着る (torso), 履く (legs/feet), かぶる (head), かける (eyewear), する (general accessories), つける (clip-on/attach). ~ている marks the resulting state of having put it on — 'is currently wearing.' ブローチ is from French 'broche,' though entered Japanese via English; some sources tag it as an English loanword.