"What do you mean, it has nothing to do?"
Susannah, hearing these words, concluded there was no connection between the two of them. If there was, with Miss Harrison's straightforward personality, she would have declared her sovereignty. It was just like how, in front of Susannah, she candidly admitted to having been in love with her brother-in-law!
If Sienna was not admitting it now, then naturally there was no connection. The earlier episode might have been nothing more than an accidental hug, or perhaps she had sprained her ankle, and Mr. Smith had merely assisted her – simple!
Once someone harbors desire, they will find reasons and excuses for this desire, in order to stifle everything that could potentially prevent it from becoming a reality!