How did Holmes convince Laura Lyons to confess?

Holmes believes Laura Lyons is the one person in the village who can help them.

‘And now tell me the result of your visit to Mrs. Laura Lyons—it was not difficult for me to guess that it was to see her that you had gone, for I am already aware that she is the one person in Coombe Tracey who might be of service to us in the matter. In fact, if you had not gone to-day it is exceedingly probable that I should have gone to-morrow.’