Star Trek: Deep Space Nine (1993) - 6x24 - Time's Orphan

Stardate: Unknown While on a nearby planet, the O'Brien family picnic is interrupted when Molly wanders off and falls into a vortex that sends her 300 years into the past. When they re-open the vortex, they try to retrieve her, but a miscalculation causes an 18-year-old Molly to appear. It is up to the crew of Deep Space Nine to try to re-educate her, while trying to find the original.