When I inquired, I found out she wasn't there.

Literal

Inquired-and-saw, she [topic-は] absent [quotative-だと] understood.

問い合わせてみて uses ~てみる ('try doing') in te-form to chain with the main clause. 不在 ('absent, not present') is a formal Sino-Japanese word. だとわかった means 'found out that.'