。
She saw many animals along the way.
Literal
She [topic-は] midway [at-で] many [possessive-の] animals [object-を] saw.
途中で ('along the way / on the way') sets the scene — this happened during a journey, not at the destination. 多くの is the prenominal form of 多い ('many'), needed because 多い cannot directly modify nouns in standard Japanese (you can't say *多い動物, only 多くの動物 or 動物が多い).