Lady Macbeth is very ambitious: ambitious to be Queen? In fact, the evidence is that her ambition is not for her own sake, but for her husband's. Consider what she says when she receives her husband's letter about what the witches have told him: her talk is all of him and the fact that he might have 'the golden round', the crown. She wants him to be King more than she wants to be Queen. This suggests she loves him.
However, her love and their relationship is not a force for good: when he wants to pull out of murdering Duncan, it is she who persuades him not to. The audience in Shakespeare's day would have been shocked to see a wife dominating a husband in such a way. Macbeth has been tempted by the witches, and now persuaded by his ruthless wife; he should have listened to his own misgivings.