。
She made a lot of mistakes typing the report.
Literal
[topic-は] report [object-を] type-doing [in-のに] many [genitive-の] mistakes [object-を] did.
~のに here is the nominalizer の plus particle に, meaning 'in (the process of) doing X' — distinct from the conjunctive ~のに ('despite, even though'), which has the same surface form. Context disambiguates them: a noun-like usage with に here, vs a clausal usage in the 'despite' sense. タイプする is loanword + する, the productive way to verbify foreign-origin nouns. 間違いをする ('make a mistake') is the standard collocation, where する pairs with 間違い as a do-verb of action.