。
She was kind enough to let me know about it.
Literal
She [topic-は] me [to-に] that matter [object-を] inform [for me-てくれる] [to the extent-ほど] kind was.
~ほど親切だ ('was kind enough to / kind to the extent of') is a productive frame for praising someone's kindness in proportion to a specific action. ほど expresses degree — 'to the extent of.' The structure [verb-clause]+ほど親切 then says 'kind enough to do X.' Note the verb tense: the main clause was past (親切だった 'was kind'), but the subordinate verb 知らせてくれる is in non-past — Japanese often keeps the embedded verb in non-past for actions whose completion isn't the focus.