What was Mr. Jellyband suspicious of? How did Sir Andrew ease his mind?

Jellyband was suspicious that Marguerite meant Sir Percy some harm... Sir Andrew's presence and his plans alleviated those suspicions by mentioning Sir Percy.

Sir Andrew had no doubt guessed the many conflicting doubts and fears which raged in honest Jellyband's head; and, as he was a gallant gentleman, he tried by this brave hint to allay some of the worthy innkeeper's suspicions. He had the satisfaction of seeing that he had partially succeeded. Jellyband's rubicund countenance brightened somewhat, at the mention of Sir Percy's name.