Her first reaction to the others' reaction to the murder was actually not well-planned. When Macduff exclaims that Duncan has been murdered, she asks, "What, in our house?" (2.3.103). This really should not be her first response to the "news" that the king has been the victim of foul play. She should probably shriek and begin to cry so that the others interpret her grief as extreme. Instead, she implies that the most important thing about the murder is that it happened in her house; she should react to the fact that the murder occurred at all. Banquo even points this out when he says, "Too cruel anywhere" (2.3.104). In other words, he subtly tells her that her response was inappropriate because it seems as though she is more worried about how this could affect her reputation than she is about her dead king.
Then, after Macduff kills the chamberlains, Lady Macbeth seems to faint, as though all of the drama is simply too much for her delicate nature to bear. The stage direction says that "Lady Macbeth is assisted to leave," immediately following line 147 in this same scene. She is, perhaps, trying to cover up her earlier faux pas in responding to the location of Duncan's murder instead of the fact of it; or maybe she's trying to draw some attention away from Macbeth since the others are not pleased with him for killing the guards who seem to have killed Duncan.