。
She was not a little surprised to hear the news.
Literal
She [topic-は] that news [object-を] heard-and not-a-little was-surprised.
少なからず ('not a little, considerably') is a literary double-negative idiom — combining the i-adjective 少ない ('few, little') with the classical negative auxiliary ず, it underlines a sense of substantial degree by formally denying a small amount. English uses the same trick with 'not a little / not insignificantly'. The construction is set, fossilized — you wouldn't construct other ~からず adverbs freely in modern Japanese, but 少なからず is alive and well in writing and elevated speech.