I see Dariana and all I can think of is Daria, which is a nice name I mostly know from a TV show like 25 years ago with the same title.
I don't know anything about your character but I assume it's purely trying to make Darren sound more fem? If you're hardset on keeping the first couple letters, you'd probably be best off just scrolling baby name sites and seeing if anything clicks, but I'll grab a couple myself: Dailyn, Dalene, Dalenna, Darrelle, Darrellyn, Darylene