According to Meilleurs Prénoms, the name Maëlys is a combination of Maëlle and Maylis. Maylis means "Mary of the Lily" (Marie à la fleur de lys). [noted -ed]
Maëlys is not a legit Breton name. The feminine form of Mael (without the dots that don't exist in Breton language) is Maela.Maëlys is a modern elaboration of Mael, inspired by another regional name: Mailys. [noted -ed]