、。。
At first glance she seems quiet, but when push comes to shove she gets it done. There's something hidden inside her.
Literal
She [topic-は] at-first-glance quiet-seeming [but-けど], do-time [topic-は] do [quotation-って] feeling. Inside [in-に] something hidden thoughts [object-を] possesses [you-know-よ].
Three Japanese moves stack here. 一見...そうだけど sets up the appearance-versus-reality frame. やる時はやる ('when she does it, she does it') is a fixed Xは X structure — repeating a verb across the topic-marker は, an emphatic idiom ('she's the type who delivers when it counts'). って感じ ('it feels like / that kind of vibe') is a casual quotative + 感じ used to soften a description into 'something like.' 中に何か秘めた思い: 秘めた is the past-form modifier of 秘める ('keep hidden inside'), which directly modifies 思い ('thoughts, feelings'). The closing よ confidently delivers the speaker's read.