Just avoid anything reminiscent of "Serenity Lane," the detox place. A longer middle name would be better than Raine or Jane, for example. Alexandra, Cecelia, etc.
Mae, Rose, Jade, Beth, Rae.
Serenity has 4 syllables so I personally would choose a shorter middle name with one syllable, but it really comes down to the sound you like. Best of luck :)