Seems made up, like a variant of
Adeline. Adalin is slightly better than Adelyn, which seems the most obvious (and trendy) spelling, and basically is
Madelyn without the M. But Adalin seems like it could or should be
Ada +
Lin = AY-dah-lin, or it also looks like it could be the name of a medication. Maybe because of Ritalin? :-/ Sorry, it's nms.