Final answer:
Suggesting that the woman lie on her left side is the appropriate intervention to help improve circulation and potentially alleviate her dizziness and light-headedness.
Step-by-step explanation:
A woman who is 32 weeks' gestation with cardiac disease and experiencing light-headedness and dizziness may benefit from an intervention that accommodates her condition. The best option among those provided for her situation could be to suggest lying on the left side. This position can help improve circulation and reduce vena cava compression, which is important as the expanding uterus can place pressure on this major vein, potentially leading to dizziness. Other options, like increased fluid intake, might also be helpful but are not specifically pointed out as interventions for these symptoms in the provided context.