What is the patient's current alignment?  Is there a residual esotropia?  If so, how much?  If her eyes are aligned, how did you determine preference?  Did the child object to occlusion of one eye?  In either case, how strongly does the child object to occlusion of the preferred eye?  Are the media clear and is the fundus normal in the non-preferred eye?

Depending on the answers to these questions, assuming that the eyes are aligned or reasonably so, and the non-preferred eye is otherwise normal you could begin patching the preferred eye.  The pattern of occlusion would depend on how closely you will be able to monitor the child.  A safe approach would be to patch the preferred eye three days and the amblyopic eye one day and re-check the child in a few weeks to a month. Otherwise you could patch the preferred eye for about half-time and re-check in a month. Patching should continue until the vision is equal as shown by visual acuity checking or fixation behavior or until there is no improvement after three months of faithful occlusion.