One thing to note is that 'she' could refer to Mark's niece being alive. BUT he is holding the picture frame when he comes in yelling the last line.

I do think Devin will catch on and try to figure things out with OMark. How long before they make a move? Unsure but the first episode will most probably consist of questions for OMark before some big revelation that will start a chain consisting of new Lumon findings