The process for unlocking Label and getting her to visit your island is quite simple - all you need to do is build the Able Sisters' shop in your town.
However, that's definitely easier said than done — check out our guide for more information on that process.
Once the clothing shop has opened in your town, Label will begin appearing in the plaza in front of Resident Services about once per week, just as her sister — Mabel — did before opening the shop.