Well, she's thrown in her lot with our side. Do you think she realises just how deeply she's in? Malfoy wouldn't protect her, if she were caught. Not for something like this. He couldn't, even if he wanted to.

Maybe she believes that Reg would have come to our side eventually, if he'd lived longer. Maybe she believes that he killed himself because it was the only way he could think of to leave the side he'd chosen.