Hello, I understand your concern. Unfortunately this is a very common occurrence with toddlers. If you are sure she only ingested one capsule, it is unlikely she will develop any life threatening effects, however, since Vyvance is basically amphetamine, it is very likely she will experience agitation, restlessness and an increased heart rate. Keep an eye on her while she has this increased energy and offer her water every now and then in order to help flush the drug out of the system. If you notice she has fever, nausea and vomiting, confusion and an erratic behavior, please contact a health facility as soon as possible. Wishing you all the best.