There's nothing magical about their first kiss. Mal's passed out on the floor of his quarters, and Inara's never been more scared. She needs to feel him, to feel some kind of closeness with him in case this is the last time she will get alone with him, the last time that she will be able to get some form of closure on their relationship. She needs to show how she feels, for if he is dead as he appears, then this is all she will ever have.
Perhaps that is what inspires her to kneel down beside him and kiss him. Or perhaps it is just adrenaline and fear, and no logic enters her mind. She's not sure which.
She just knows that she does it - she kisses him - and it is then that she realises her mistake. He's not dead. And worse, he's a victim of the goodnight kiss, a narcotic she is familiar with and should have suspected when she saw his prone, but seemingly unblemished form. She curses before she hits the floor beside him, knowing full well that the rest of the crew might now be clued in on her emotional attachments to Mal.
When the room solidifies around her once more, and the crew are gathered around her and Mal, she blinks through the cloud now hovering in her head and tries to act normal.
Zoe has a look about her like she knows.
Inara curses herself inwardly. No, nothing about their first kiss is magical at all. If anything, their first kiss has been one of the most stressful moments Inara has dealt with lately - and that includes the crew's most recent fire fight.